Deck 4: Forces and Newtons Laws of Motion

Question 1

A 2150-kg truck is traveling along a straight, level road at a constant speed of 55.0 km/h when the driver removes his foot from the accelerator. After 21.0 s, the truck's speed is 33.0 km/h. What is the magnitude of the average net force acting on the truck during the 21.0 s interval?

A)2250 N
B)626 N
C)1890 N
D)972 N
E)229 N

Answer 1

626 N

Question 2

A 2.0-kg object moves in a straight line on a horizontal frictionless surface.
The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object.
Which section(s) of the graph corresponds to a condition of zero net force?

A)V only
B)III only
C)II and IV
D)II, III, and IV
E)I, III, and V

Answer 2

II and IV

Question 3

When the net force that acts on a hockey puck is 12 N, the puck accelerates at a rate of 48 m/s². Determine the mass of the puck.

A)0.25 kg
B)1.0 kg
C)5.0 kg
D)2.5 kg
E)2.0 kg

Answer 3

0.25 kg

Question 4

A net force of 25 N is applied for 5.7 s to a 12-kg box initially at rest. What is the speed of the box at the end of the 5.7-s interval?

A)1.8 m/s
B)12 m/s
C)3.0 m/s
D)7.5 m/s
E)30 m/s

Question 5

Complete the following statement: The term net force most accurately describes

A)the mass of an object
B)the inertia of an object.
C)the quantity that causes a displacement.
D)the quantity that keeps an object moving.
E)the quantity that changes the velocity of an object.

Question 6

An apple crate with a weight of 225 N accelerates along a frictionless surface as the crate is pulled with a force of 14.5 N as shown in the drawing. What is the horizontal acceleration of the crate?

A)1.40 m/s²
B)0.427 m/s²
C)1.29 m/s²
D)0.597 m/s²
E)0.644 m/s²

Question 7

Two forces act on a 4.5-kg block resting on a frictionless surface as shown. What is the magnitude of the horizontal acceleration of the block?

A)1.8 m/s²
B)1.2 m/s²
C)0.82 m/s²
D)3.2 m/s²
E)8.9 m/s²

Question 8

The graph shows the velocities of two objects of equal mass as a function of time. Net forces F_A, F_B, and F_C acted on the objects during intervals A, B, and C, respectively. Which one of the following choices is the correct relationship between the magnitudes of the net forces?

A)F_B = F_C > F_A
B)F_C > F_B > F_A
C)F_A > F_B = F_C
D)F_A = F_B = F_C
E)F_A > F_B > F_C

Question 9

The figure shows the velocity versus time curve for a car traveling along a straight line. Which of the following statements is false?

A)No net force acts on the car during interval B.
B)Net forces act on the car during intervals A and C.
C)Opposing forces may be acting on the car during interval B.
D)Opposing forces may be acting on the car during interval C.
E)The magnitude of the net force acting during interval A is less than that during C.

Question 10

A 2.0-kg object moves in a straight line on a horizontal frictionless surface.
The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object.
In which section(s) of the graph is the net force changing?

A)I and III
B)II and IV
C)III
D)IV
E)I and V

Question 11

A 975-kg car accelerates from rest to 26.7 m/s in a distance of 120 m. What is the magnitude of the average net force acting on the car?

A)740 N
B)2900 N
C)91 N
D)1300 N
E)7900 N

Question 12

With one exception, each of the following units can be used to express mass. What is the exception?

A)newton
B)slug
C)gram
D)N•s²/m
E)kilogram

Question 13

Complete the following statement: An inertial reference frame is one in which

A)Newton's first law of motion is valid.
B)the inertias of objects within the frame are zero.
C)the frame is accelerating.
D)the acceleration due to gravity is greater than zero m/s².
E)Newton's second law of motion is not valid.

Question 14

Two forces act on a hockey puck. For which orientation of the forces will the puck acquire an acceleration with the largest magnitude?

A)
B)
C)
D)
E)The magnitude of the acceleration will be the same in all four cases shown above.

Question 15

An object moves due east at constant speed. A net force directed due north then acts on the object for 5.0 s. At the end of the 5.0-second period, the net force drops to zero newtons. Which one of the following statements is necessarily true?

A)The object will be moving eastward when the force drops to zero newtons.
B)The change in the velocity of the object is directed north of west.
C)The direction of the object's acceleration depends on how fast the object was initially moving.
D)The final velocity of the object is directed north of east.
E)The magnitude of the object's acceleration depends on how fast the object was initially moving.

Question 16

A 2.0-kg object moves in a straight line on a horizontal frictionless surface.
The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object.
Which section of the graph corresponds to the application of the largest constant net force?

A)I
B)II
C)III
D)IV
E)V

Question 17

A net force is required to give an object with mass m an acceleration a. If a net force 6 is applied to an object with mass 2m, what is the acceleration on this object?

A)
B)2
C)3
D)4
E)6

Question 18

Which one of the following terms is used to indicate the natural tendency of an object to remain at rest or in motion at a constant speed along a straight line?

A)velocity
B)inertia
C)acceleration
D)equilibrium
E)force

Question 19

Two forces act on a 16-kg object. The first force has a magnitude of 68 N and is directed 24° north of east. The second force is 32 N, 48° north of west. What is the acceleration of the object resulting from the application of these two forces to the object?

A)1.6 m/s², 5.5° north of east
B)1.9 m/s², 18° north of west
C)2.4 m/s², 34° north of east
D)3.6 m/s², 5.5° north of west
E)4.1 m/s², 52° north of east

Question 20

A 2.0-kg object moves in a straight line on a horizontal frictionless surface.
The graph shows the velocity of the object as a function of time. The various equal time intervals are labeled using Roman numerals: I, II, III, IV, and V. The net force on the object always acts along the line of motion of the object.
In which section of the graph is the magnitude of the net force decreasing?

A)I
B)II
C)III
D)IV
E)V

Question 21

A horse pulls a cart along a flat road. Consider the following four forces that arise in this situation.
(1) the force of the horse pulling on the cart
(2) the force of the cart pulling on the horse
(3) the force of the horse pushing on the road
(4) the force of the road pushing on the horse
Which two forces form an "action-reaction" pair that obeys Newton's third law?

A)1 and 4
B)1 and 3
C)2 and 4
D)3 and 4
E)2 and 3

Question 22

Which one of the following statements concerning this situation is true?

A)The spacecraft does not move, but the astronaut moves to the right with a constant speed.
B)The astronaut stops moving after he stops pushing on the spacecraft.
C)The force exerted on the astronaut is larger than the force exerted on the spacecraft.
D)The force exerted on the spacecraft is larger than the force exerted on the astronaut.
E)The velocity of the astronaut increases while he is pushing on the spacecraft.

Question 23

Two point masses m and M are separated by a distance d. If the distance between the masses is increased to 3d, how does the gravitational force between them change?

A)The force will be one-third as great.
B)The force will be one-ninth as great.
C)The force will be three times as great.
D)The force will be nine times as great.
E)It is impossible to determine without knowing the numerical values of m, M, and d.

Question 24

A rock is thrown straight up from the earth's surface. Which one of the following statements concerning the net force acting on the rock at the top of its path is true?

A)The net force is equal to the weight of the rock.
B)The net force is instantaneously equal to zero newtons.
C)The direction of the net force changes from up to down.
D)The net force is greater than the weight of the rock.
E)The net force is less than the weight of the rock, but greater than zero newtons.

Question 25

A marble is dropped straight down from a distance h above the floor. Let F_m = the magnitude of the gravitational force on the marble due to the earth;
F_e = the magnitude of the gravitational force on the earth due to the marble;
A_m = the magnitude of the acceleration of the marble toward the earth;
A_e = the magnitude of the acceleration of the earth toward the marble.
Which set of conditions is true as the marble falls toward the earth? Neglect any effects of air resistance.

A)F_m = F_e and a_m < a_e
B)F_m < F_e and a_m > a_e
C)F_m < F_e and a_m = a_e
D)F_m > F_e and a_m = a_e
E)F_m = F_e and a_m > a_e

Question 26

A physics student in a hot air balloon ascends vertically at constant speed. Consider the following four forces present in this situation:

11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 1= the weight of the hot air balloon
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 3= the force of the student pulling on the earth
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 2= the weight of the student
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 4= the force of the hot air balloon pulling on the student
Which two forces form an "action-reaction" pair that obeys Newton's third law?

A) ₁ and ₂
B) ₂ and ₃
C) ₁ and ₃
D) ₂ and ₄
E) ₃ and ₄

Question 27

An astronaut orbits the earth in a space capsule whose height above the earth is equal to the earth's radius. How does the mass of the astronaut in the capsule compare to her mass on the earth?

A)Her mass is equal to her mass on earth.
B)Her mass is approximately equal to one-fourth her mass on earth.
C)Her mass is approximately equal to one-half of her mass on earth.
D)Her mass is approximately equal to one-third of her mass on earth.
E)Her mass is approximately equal to one-sixteenth her mass on earth.

Question 28

What is the weight of a 2.50-kg bag of sand on the surface of the earth?

A)2.50 N
B)9.80 N
C)24.5 N
D)49.0 N
E)98.0 N

Question 29

Which one of the following statements concerning the two "gravitational constants" G, the universal gravitational constant, and g the magnitude of the acceleration due to gravity is true?

A)The values of g and G depend on location.
B)The values of g and G do not depend on location.
C)The value of G is the same everywhere in the universe, but the value of g is not.
D)The value of g is the same everywhere in the universe, but the value of G is not.
E)The values of g and G are equal on the surface of any planet, but in general, G varies with location in the universe.

Question 30

Two satellites of different masses are in the same circular orbit around the earth. Which one of the following statements is true concerning the magnitude of the gravitational force that acts on each of them?

A)The magnitude of the gravitational force is zero newtons for both satellites.
B)The magnitude of the gravitational force is the same for both satellites, but not zero newtons.
C)The magnitude of the gravitational force is zero newtons for one, but not for the other.
D)The magnitude of the gravitational force depends on their masses.
E)The magnitude of the gravitational force varies from point to point in their orbits.

Question 31

Consider the following forces. (1) frictional (2) gravitational (3) tension (4) strong nuclear (5) normal (6) electroweak
Which of the forces listed are considered fundamental forces?

A)1, 2, and 4
B)1, 2, 3, and 5
C)1, 3, and 5
D)2, 4, and 6
E)2, 3, 4, and 6

Question 32

Which one of the following statements best explains why the weight of an object of mass m is different on Mars than it is on the Earth?

A)The mass of Mars is different from that of Earth.
B)The masses and radii of Mars and Earth are not the same.
C)The mass m is further from the Earth's center when it is on Mars.
D)The constant G is different on Mars.
E)The mass m will be different on Mars.

Question 33

A horse pulls a cart along a flat road. Consider the following four forces that arise in this situation.
(1) the force of the horse pulling on the cart
(2) the force of the cart pulling on the horse
(3) the force of the horse pushing on the road
(4) the force of the road pushing on the horse

-Suppose that the horse and cart have started from rest; and as time goes on, their speed increases in the same direction. Which one of the following conclusions is correct concerning the magnitudes of the forces mentioned above?

A)Force 1 exceeds force 2.
B)Force 2 is less than force 3.
C)Force 2 exceeds force 4.
D)Force 3 exceeds force 4.
E)Forces 1 and 2 cannot have equal magnitudes.

Question 34

The book has an acceleration of 0 m/s². Which pair of forces, excluding "action-reaction" pairs, must be equal in magnitude and opposite in direction?

A)1 and 2
B)1 and 3
C)1 and 4
D)2 and 3
E)2 and 4

Question 35

An astronaut orbits the earth in a space capsule whose height above the earth is equal to the earth's radius. How does the weight of the astronaut in the capsule compare to her weight on the earth?

A)Her weight is equal to zero newtons.
B)Her weight is approximately equal to one-fourth her weight on earth.
C)Her weight is approximately equal to one-half of her weight on earth.
D)Her weight is approximately equal to one-third of her weight on earth.
E)Her weight is approximately equal to one-sixteenth her weight on earth.

Question 36

Determine the magnitude of the acceleration of the spacecraft.

A)51.4 m/s²
B)0.36 m/s²
C)2.5 × 10^-3 m/s²
D)7.0 × 10^-3 m/s²
E)3.97 × 10^-4 m/s²

Question 37

Two point masses m and M are separated by a distance d. If the separation d remains fixed and the masses are increased to the values 3m and 3M respectively, how does the gravitational force between them change?

A)The force will be one-third as great.
B)The force will be one-ninth as great.
C)The force will be three times as great.
D)The force will be nine times as great.
E)It is impossible to determine without knowing the numerical values of m, M, and d.

Question 38

A 2.00-kg projectile is fired at an angle of 20.0°. What is the magnitude of the force exerted on the projectile when it is at the highest position in its trajectory? Neglect any effects of air resistance.

A)19.6 N
B)14.7 N
C)9.80 N
D)4.90 N
E)0 N

Question 39

A physics student in a hot air balloon ascends vertically at constant speed. Consider the following four forces present in this situation:

11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 1= the weight of the hot air balloon
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 3= the force of the student pulling on the earth
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 2= the weight of the student
11ec874b_21ea_ddf1_a44c_811fc40246c2_TB34225555_11 4= the force of the hot air balloon pulling on the student
Which one of the following relationships concerning the forces or their magnitudes is true?

A)F₄ > F₂
B)F₁ < F₂
C)F₄ > F₁
D) ₂ = - ₄
E) ₃ = - ₄

Question 40

Which two forces form an "action-reaction" pair that obeys Newton's third law?

A)1 and 2
B)1 and 3
C)1 and 4
D)2 and 4
E)3 and 4

Question 41

Two blocks rest on a horizontal frictionless surface as shown. The surface between the top and bottom blocks is roughened so that there is no slipping between the two blocks. A 30-N force is applied to the bottom block as suggested in the figure.
What is the force of static friction between the top and bottom blocks?

A)zero newtons
B)10 N
C)20 N
D)25 N
E)30 N

Question 42

A 44-kg child steps onto a scale and the scale reads 430 N. What is the magnitude of the normal force acting on the child?

A)44 N
B)215 N
C)430 N
D)645 N
E)860 N

Question 43

A 2.0-N force acts horizontally on a 10-N block that is initially at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50.
Suppose that the block now moves across the surface with constant speed under the action of a horizontal 3.0-N force. Which one of the following statements concerning this situation is false?

A)The block is not accelerated.
B)The net force on the block is zero newtons.
C)The frictional force on the block has magnitude 3.0 N.
D)The coefficient of kinetic friction between the block and the surface is 0.30.
E)The direction of the total force that the surface exerts on the block is vertically upward.

Question 44

A 8-kg block is set moving with an initial speed of 6 m/s on a rough horizontal surface. If the force of friction is 12 N, approximately how far does the block travel before it stops?

A)1.5 m
B)3 m
C)6 m
D)9 m
E)12 m

Question 45

A crate rests on the flatbed of a truck that is initially traveling at 15 m/s on a level road. The driver applies the brakes and the truck is brought to a halt in a distance of 38 m. If the deceleration of the truck is constant, what is the minimum coefficient of friction between the crate and the truck that is required to keep the crate from sliding?

A)0.20
B)0.30
C)0.39
D)0.59
E)This cannot be determined without knowing the mass of the crate.

Question 46

. The figure shows the free-body diagram for the block. represents the normal force on the block; and represents the force of kinetic friction.
If the coefficient of kinetic friction, , between the block and the surface is 0.30 and the magnitude of the frictional force is 80.0 N, what is the weight of the block?

A)1.6 N
B)4.0 N
C)160 N
D)270 N
E)410 N

Question 47

. The figure shows the free-body diagram for the block. represents the normal force on the block; and represents the force of kinetic friction.
What is the magnitude of ?

A)2mg
B)P
C)f
D)mg
E)This cannot be determined from the information given.

Question 48

pulls on a crate of mass m that is in contact with a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation. represents the weight of the crate. represents the normal force on the crate, and represents the frictional force.
Which statement best describes the motion of the crate?

A)The crate must be at rest.
B)The crate must be moving with constant velocity.
C)The crate must be moving with constant acceleration.
D)The crate may be either at rest or moving with constant velocity.
E)The crate may be either at rest or moving with constant acceleration.

Question 49

Two blocks rest on a horizontal frictionless surface as shown. The surface between the top and bottom blocks is roughened so that there is no slipping between the two blocks. A 30-N force is applied to the bottom block as suggested in the figure.
What is the minimum coefficient of static friction necessary to keep the top block from slipping on the bottom block?

A)0.05
B)0.10
C)0.20
D)0.30
E)0.40

Question 50

A 2.0-N force acts horizontally on a 10-N block that is initially at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50.
What is the magnitude of the frictional force that acts on the block?

A)0 N
B)2 N
C)5 N
D)8 N
E)10 N

Question 51

Two blocks rest on a horizontal frictionless surface as shown. The surface between the top and bottom blocks is roughened so that there is no slipping between the two blocks. A 30-N force is applied to the bottom block as suggested in the figure.
What is the acceleration of the "two block" system?

A)1 m/s²
B)2 m/s²
C)3 m/s²
D)6 m/s²
E)15 m/s²

Question 52

Note the following situations: In which case will the magnitude of the normal force on the block be equal to (Mg + F sin $\theta$ )?

A)case 1 only
B)case 2 only
C)both cases 1 and 2
D)both cases 2 and 3
E)cases 1, 2, and 3

Question 53

A boy pulls a 5.0-kg sled with a rope that makes a 60.0° angle with respect to the horizontal surface of a frozen pond. The boy pulls on the rope with a force of 10.0 N; and the sled moves with constant velocity. What is the coefficient of friction between the sled and the ice?

A)0.09
B)0.12
C)0.18
D)0.06
E)0.24

Question 54

What is the magnitude of the gravitational force acting on a 79.5-kg student due to a 58.0-kg student sitting 2.40 m away in the classroom?

A)3.14 × 10^-9 N
B)5.33 × 10^-8 N
C)7.91 × 10^-10 N
D)1.41 × 10^-7 N
E)6.29 × 10^-8 N

Question 55

pulls on a crate of mass m that is in contact with a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation. represents the weight of the crate. represents the normal force on the crate, and represents the frictional force.
What is the magnitude of , the normal force on the crate?

A)57 N
B)80 N
C)160 N
D)196 N
E)230 N

Question 56

Two identical blocks are pulled along a rough surface as suggested in the figure. Which one of the following statements is false?

A)The coefficient of kinetic friction is the same in each case.
B)A force of the same magnitude is needed to keep each block moving.
C)A force of the same magnitude was required to start each block moving.
D)The normal force exerted on the blocks by the surface is the same for both blocks.
E)The magnitude of the force of kinetic friction is greater for the block on the right.

Question 57

In an experiment with a block of wood on an inclined plane, with dimensions shown in the figure, the following observations are made: (1) If the block is placed on the inclined plane, it remains there at rest. (2) If the block is given a small push, it will accelerate toward the bottom of the incline without any further pushing.
Which one of the following statements is the best conclusion that can be drawn from these observations?

A)The coefficient of kinetic friction must be negative.
B)Both coefficients of friction must be less than 0.25.
C)Both coefficients of friction must be greater than 0.25.
D)The coefficient of static friction must be less than the coefficient of kinetic friction.
E)The coefficient of static friction is greater than 0.25 while the coefficient of kinetic friction is less than 0.25.

Question 58

A 250-N force is directed horizontally as shown to push a 29-kg box up an inclined plane at a constant speed. Determine the magnitude of the normal force, F_N, and the coefficient of kinetic friction, µ_k. F_N µ_k

A)330 N 0.31
B)310 N 0.33
C)250 N 0.27
D)290 N 0.30
E)370 N 0.26

Question 59

The wheels of an automobile are locked as it slides to a stop from an initial speed of 30.0 m/s. If the coefficient of kinetic friction is 0.600 and the road is horizontal, approximately how long does it take the car to stop?

A)4.22 s
B)5.10 s
C)8.75 s
D)10.4 s
E)15.3 s

Question 60

A 2.0-N rock slides on a frictionless inclined plane. Which one of the following statements is true concerning the normal force that the plane exerts on the rock?

A)The normal force is zero newtons.
B)The normal force is 2.0 N.
C)The normal force is less than 2.0 N, but greater than zero newtons.
D)The normal force is greater than 2.0 N.
E)It increases as the angle of inclination, $\theta$ , is increased.

Question 61

A 20-kg crate is suspended from a fixed, horizontal beam by two vertical ropes. What is the approximate tension in each rope?

A)10 N
B)40 N
C)100 N
D)200 N
E)390 N

Question 62

A rock is suspended from a string; and it moves downward at constant speed. Which one of the following statements is true concerning the tension in the string if air resistance is not ignored?

A)The tension is zero newtons.
B)The tension points downward.
C)The tension is equal to the weight of the rock.
D)The tension is less than the weight of the rock.
E)The tension is greater than the weight of the rock.

Question 63

What is the tension in the right-hand cable?

A)87 N
B)150 N
C)170 N
D)260 N
E)300 N

Question 64

A rock is suspended from a string and moves downward at constant speed. Which statement is true concerning the tension in the string if air resistance is ignored?

A)The tension is zero newtons.
B)The tension points downward.
C)The tension is equal to the weight of the rock.
D)The tension is less than the weight of the rock.
E)The tension is greater than the weight of the rock.

Question 65

A woman stands on a bathroom scale in an elevator that is not moving. The scale reads 500 N. The elevator then moves downward at a constant velocity of 5 m/s. What does the scale read while the elevator descends with constant velocity?

A)100 N
B)250 N
C)500 N
D)600 N
E)750 N

Question 66

A rope connects boat A to boat B. Boat A starts from rest and accelerates to a speed of 9.5 m/s in a time t = 47 s. The mass of boat B is 540 kg. Assuming a constant frictional force of 230 N acts on boat B, what is the magnitude of the tension in the rope that connects the boats during the time that boat A is accelerating?

A)340 N
B)1270 N
C)230 N
D)860 N
E)160 N

Question 67

Two sleds are hooked together in tandem as shown in the figure. The front sled is twice as massive as the rear sled. The sleds are pulled along a frictionless surface by an applied force . The tension in the rope between the sleds is .
Determine the ratio of the magnitudes of the two forces, .

A)0.25
B)0.33
C)0.50
D)0.67
E)2.0

Question 68

A rock is suspended from a string; and it accelerates upward. Which statement is true concerning the tension in the string?

A)The tension points downward.
B)The tension is less than the weight of the rock.
C)The tension is equal to the weight of the rock.
D)The tension is greater than the weight of the rock.
E)The tension is independent of the magnitude of the rock's acceleration.

Question 69

A block of mass M is held motionless on a frictionless inclined plane by means of a string attached to a vertical wall as shown in the drawing.

-If the string breaks, what is the magnitude of the acceleration of the block as it slides down the inclined plane?

A)zero m/s²
B)g
C)g cos $\theta$
D)g sin $\theta$
E)g tan $\theta$

Question 70

In a tug-of-war, each man on a 5-man team pulls with an average force of 500 N. What is the tension in the center of the rope?

A)zero newtons
B)100 N
C)500 N
D)2500 N
E)5000 N

Question 71

A block of weight W is suspended by a string of fixed length. The ends of the string are held at various positions as shown in the figures below. In which case, if any, is the magnitude of the tension along the string the largest?

A)case A
B)case B
C)case C
D)case D
E)The magnitude of the tension will be the same in all four cases, since the string must support the entire weight of the block.

Question 72

What is the tension in the horizontal cable?

A)87 N
B)150 N
C)170 N
D)260 N
E)300 N

Question 73

A block of mass M is held motionless on a frictionless inclined plane by means of a string attached to a vertical wall as shown in the drawing.

-What is the magnitude of the tension in the string?

A)zero newtons
B)Mg
C)Mg cos $\theta$
D)Mg sin $\theta$
E)Mg tan $\theta$

Question 74

A muscle builder holds the ends of a massless rope. At the center of the rope, a 7.9-kg ball is hung as shown. What is the tension in the rope if the angle $\theta$ in the drawing is 6.0°?

A)960 N
B)740 N
C)370 N
D)230 N
E)150 N

Question 75

A rock is suspended from a string; and it accelerates downward. Which one of the following statements concerning the tension in the string is true?

A)The tension points downward.
B)The tension is less than the weight of the rock.
C)The tension is equal to the weight of the rock.
D)The tension is greater than the weight of the rock.
E)The tension is independent of the magnitude of the rock's acceleration.

Question 76

A small plane climbs with a constant velocity of 240 m/s at an angle of 24° with respect to the horizontal. Which statement is true concerning the magnitude of the net force on the plane?

A)It is equal to zero newtons.
B)It is equal to the weight of the plane.
C)It is equal to the magnitude of the force of air resistance.
D)It is less than the weight of the plane but greater than zero newtons.
E)It is equal to the component of the weight of the plane in the direction of motion.

Question 77

Under what condition(s) will an object be in equilibrium?

A)If the object is either at rest or moving with constant velocity, it is in equilibrium.
B)If the object is either moving with constant velocity or with constant acceleration, it is in equilibrium.
C)Only if the object is at rest can it be in equilibrium.
D)Only if the object is moving with constant velocity can it be in equilibrium.
E)Only if the object is moving with constant acceleration can it be in equilibrium.

Question 78

A block of mass M is held motionless on a frictionless inclined plane by means of a string attached to a vertical wall as shown in the drawing.

-Assume the plane is not frictionless and the string breaks, what minimum value of the coefficient of static friction, $\mu$ _s, would prevent the block from sliding down the inclined plane?

A)zero
B)1
C)cos $\theta$
D)sin $\theta$
E)tan $\theta$

Question 79

A block of mass M is hung by ropes as shown. The system is in equilibrium. The point O represents the knot, the junction of the three ropes. Which of the following statements is true concerning the magnitudes of the three forces in equilibrium?

A)
B)
C)
D)
E)

Question 80

A 4-kg block is connected by means of a massless rope to a 2-kg block as shown in the figure. Complete the following statement: If the 4-kg block is to begin sliding, the coefficient of static friction between the 4-kg block and the surface must be

A)less than zero.
B)greater than 2.
C)greater than 1, but less than 2.
D)greater than 0.5, but less than 1.
E)less than 0.5, but greater than zero.