Deck 4: Forces and Newtons Laws

Question 1

A book is placed on a chair. Then a videocassette is placed on the book. The floor exerts a normal force:

A)on all three.
B)only on the book.
C)only on the chair.
D)upwards on the chair and downwards on the book.
E)only on the objects that you have defined to be part of the system.

Answer 1

only on the chair.

Question 2

If M = 2.0 kg, what is the tension in string 1?

A)1.2 N
B)11 N
C)34 N
D)3.5 N
E)40 N

Answer 2

34 N

Question 3

A person weighing 0.70 kN rides in an elevator that has an upward acceleration of 1.5 m/s2. What is the magnitude of the force of the elevator floor on the person?

A)0.11 kN
B)0.81 kN
C)0.70 kN
D)0.59 kN
E)0.64 kN

Answer 3

0.81 kN

Question 4

A juggler throws two balls up to the same height so that they pass each other halfway up when A is rising and B is descending. Ignore air resistance and buoyant forces. Which statement is true of the two balls at that point?

A)There is a residual upward force from the hand on each ball.
B)There is a greater residual force from the hand on A than there is on B.
C)Only gravity acts on B but there is an additional residual force from the hand on A.
D)There is an additional downwards force besides gravity on each ball.
E)The only force acting on each ball is the gravitational force.

Question 5

A block is pushed up a frictionless 30 $\degree$ incline by an applied force as shown. If F = 25 N and M = 3.0 kg, what is the magnitude of the resulting acceleration of the block?

A)2.3 m/s2
B)4.6 m/s2
C)3.5 m/s2
D)2.9 m/s2
E)5.1 m/s2

Question 6

The horizontal surface on which the block slides is frictionless. If F = 20 N and M = 5.0 kg, what is the magnitude of the resulting acceleration of the block?

A)5.3 m/s2
B)6.2 m/s2
C)7.5 m/s2
D)4.7 m/s2
E)3.2 m/s2

Question 7

A 3.0-kg block slides on a frictionless 20 $\degree$ inclined plane. A force of 16 N acting parallel to the incline and up the incline is applied to the block. What is the acceleration of the block?

A)2.0 m/s2 down the incline
B)5.3 m/s2 up the incline
C)2.0 m/s2 up the incline
D)3.9 m/s2 down the incline
E)3.9 m/s2 up the incline

Question 8

Only two forces act on a 3.0-kg mass. One of the forces is 9.0 N east, and the other is 8.0 N in the direction of 62 $\degree$ north of west. What is the magnitude of the acceleration of the mass?

A)2.0 m/s2
B)2.4 m/s2
C)3.3 m/s2
D)2.9 m/s2
E)5.7 m/s2

Question 9

A 1.5-kg object has a velocity of 5 $\hat{\mathbf{j}}$ m/s at t = 0. It is accelerated at a constant rate for five seconds after which it has a velocity of (6 $\hat{\mathbf{i}}$ + 12 $\hat{\mathbf{j}}$ ) m/s. What is the direction of the resultant force acting on the object during this time interval?

A)65 $\degree$
B)56 $\degree$
C)61 $\degree$
D)49 $\degree$
E)27 $\degree$

Question 10

If $\alpha$ = 40 $\degree$ and the tension in string 2 is 30 N, determine M.

A)3.4 kg
B)3.6 kg
C)2.6 kg
D)4.9 kg
E)7.5 kg

Question 11

A bumper car in Luna Park is moving at constant velocity when another bumper car starts to push on it with a constant force at an angle of 60° with respect to the first car's initial velocity. The second bumper car continues pushing in exactly that direction for some time. What is most likely to happen is that:

A)the first car will stop moving.
B)the first car will move in the direction of the force.
C)the first car's velocity will increase in magnitude but not change direction.
D)the first car's velocity will gradually change direction more and more toward that of the force while increasing in magnitude.
E)the first car's velocity will gradually change direction more and more toward that of the force while decreasing in magnitude.

Question 12

A 1.5-kg object has a velocity of 5 $\hat{\mathbf{j}}$ m/s at t = 0. It is accelerated at a constant rate for five seconds after which it has a velocity of (6 $\hat{\mathbf{i}}$ + 12 $\hat{\mathbf{j}}$ ) m/s. What is the magnitude of the resultant force acting on the object during this time interval?

A)3.8 N
B)3.2 N
C)2.8 N
D)4.3 N
E)4.6 N

Question 13

When the vector sum of three co-planar forces, $\vec{A}$ , $\overrightarrow{\mathbf{B}}$ and $\overrightarrow{\mathbf{C}}$ , is parallel to $\vec{A}$ , we can conclude that $\overrightarrow{\mathbf{B}}$ and $\overrightarrow{\mathbf{C}}$ :

A)must sum to zero.
B)must be equal and opposite.
C)must have equal and opposite components perpendicular to $\vec{A}$ .
D)must have equal and opposite components parallel to $\vec{A}$ .
E)must have equal and opposite components parallel and perpendicular to $\vec{A}$ .

Question 14

The apparent weight of a fish in an elevator is greatest when the elevator:

A)moves downward at constant velocity.
B)moves upward at constant velocity.
C)accelerates downward.
D)accelerates upward.
E)is not moving.

Question 15

A constant force F is applied to a body of mass m that initially is headed east at velocity v0 until its velocity becomes -v0. The total time of travel is 2t. The total distance the body travels in that time is:

A) $\frac{1}{2} \frac{F}{m} t^{2}$ .
B) $\frac{F}{m} t^{2}$ .
C) $v_{0} t-\frac{1}{2} \frac{F}{m} t^{2}$ .
D) $v_{0} t+\frac{1}{2} \frac{F}{m} t^{2}$ .
E) $2\left(v_{0} t+\frac{1}{2} \frac{F}{m} t^{2}\right)$ .

Question 16

A heavy weight is supported by two cables that exert tensions of magnitude T1 and T2. Which statement is correct?

A)T1 = T2.
B)T1y = T2y.
C)T1 > T2.
D)T1 < T2.
E)We need the mass of the box in order to determine the correct answer.

Question 17

The only two forces acting on a body have magnitudes of 20 N and 35 N and directions that differ by 80 $\degree$ . The resulting acceleration has a magnitude of 20 m/s2. What is the mass of the body?

A)2.4 kg
B)2.2 kg
C)2.7 kg
D)3.1 kg
E)1.5 kg

Question 18

A 5.0-kg object is suspended by a string from the ceiling of an elevator that is accelerating downward at a rate of 2.6 m/s2. What is the tension in the string?

A)49 N
B)36 N
C)62 N
D)13 N
E)52 N

Question 19

If M = 1.1 kg, what is the tension in string 1?

A)54 N
B)47 N
C)40 N
D)62 N
E)57 N

Question 20

The first of two identical boxes of mass m is sitting on level ground. The second box is sitting on a ramp that makes a 20 $\degree$ angle with the ground. The normal force of the level ground on the first box is NL; the normal force of the ramp on the second box is NR. Which statement is correct?

A)NR = NL = mg.
B)NL = mg; NR = mg sin 20 $\degree$ .
C)NL = mg; NR = mg cos 20 $\degree$ .
D)NL = mg; NR = -mg cos 20 $\degree$ .
E)NR = -NL = -mg.

Question 21

A 70-kg stunt artist rides in a rocket sled which slides along a flat inclined surface. At an instant when the sled's acceleration has a horizontal component of 6.0 m/s2 and a downward component of 2.8 m/s2, what is the magnitude of the force on the rider by the sled?

A)0.83 kN
B)0.98 kN
C)0.65 kN
D)0.68 kN
E)0.72 kN

Question 22

A 5.0-kg mass sits on the floor of an elevator in a Gold Coast skyscraper. The elevator has a downward acceleration of 1.0 m/s2. On top of the 5.0-kg mass is an object of unknown mass. The force of the elevator on the 5.0-kg mass is 80 N up. Determine the unknown mass.

A)3.3 kg
B)2.4 kg
C)1.6 kg
D)4.1 kg
E)5.0 kg

Question 23

If F = 40 N and M = 1.5 kg, what is the tension in the string connecting M and 2M? Assume that all surfaces are frictionless.

A)13 N
B)23 N
C)36 N
D)15 N
E)28 N

Question 24

The horizontal surface on which the objects slide is frictionless. If F = 12 N, what is the tension in string 1?

A)35 N
B)30 N
C)40 N
D)45 N
E)25 N

Question 25

Two people, each of 70 kg mass, are riding in an elevator. One is standing on the floor. The other is hanging on a rope suspended from the ceiling. Compare the force $\overrightarrow{\mathbf{F}}_{{F}}$ the floor exerts on the first person to the force $\overrightarrow{\mathbf{F}}_{{R}}$ the rope exerts on the second person. Which statement is correct?

A)They are equal and opposite in direction.
B)They are equal and have the same direction.
C) $\overrightarrow{\mathbf{F}}_{{R}}$ is greater than $\overrightarrow{\mathbf{F}}_{{F}}$ , but they have the same direction.
D) $\overrightarrow{\mathrm{F}}_{R}$ is greater than $\overrightarrow{\mathbf{F}}_{{F}}$ , but they have opposite directions.
E) $\overrightarrow{\mathrm{F}}_{R}$ is less than $\overrightarrow{\mathbf{F}}_{{F}}$ , but they have the same direction.

Question 26

The surface of the inclined plane shown is frictionless. If F = 30 N, what is the magnitude of the force exerted on the 3.0-kg block by the 2.0-kg block?

A)18 N
B)27 N
C)24 N
D)21 N
E)15 N

Question 27

When you drag a toy teddy bear along the floor by a force that is parallel to the floor, the magnitude of the force of friction:

A)is independent of velocity or acceleration.
B)increases when the velocity increases.
C)is proportional to the acceleration.
D)decreases when the force parallel to the floor increases.
E)increases when the force parallel to the floor increases.

Question 28

Three boxes are pushed across a frictionless horizontal surface as shown. When we compare the normal force N2,5 that mass 2m exerts on mass 5m with the normal force N5,10 that mass 5m exerts on mass 10m, we find that:

A)N2,5 = N5,10 = F.
B)N2,5 = F > N5,10.
C)F > N2,5 = N5,10.
D)F > N2,5 > N5,10.
E)F > N5,10 > N2,5.

Question 29

If F = 8.0 N and M = 1.0 kg, what is the tension in the connecting string? The pulley and all surfaces are frictionless.

A)4.1 N
B)3.5 N
C)3.8 N
D)3.1 N
E)4.8 N

Question 30

If F = 5.0 N, what is the magnitude of the force exerted by block 2 on block 1?

A)17 N
B)19 N
C)21 N
D)23 N
E)5.0 N

Question 31

If the tension, T, is 15 N and the magnitude of the acceleration, a, is 3.0 m/s2, what is the mass, m, of the suspended object? Assume that all surfaces and the pulley are frictionless.

A)3.1 kg
B)2.5 kg
C)2.8 kg
D)2.2 kg
E)3.7 kg

Question 32

An astronaut who weighs 800 N on the surface of the earth lifts off from planet Zuton in a space ship. The free-fall acceleration on Zuton is 3.0 m/s2 (down). At the moment of liftoff the acceleration of the space ship is 0.50 m/s2 (up). What is the magnitude of the force of the space ship on the astronaut?

A)41 N
B)0.29 kN
C)0.24 kN
D)0.20 kN
E)0.37 kN

Question 33

You hold a tennis racket in your hand. On top of the racket you have balanced a ball. Which statement is true?

A)The force of your hand on the racket and the force of the ball on the racket are equal and opposite.
B)The force of the racket on your hand and the force of the ball on the racket are equal and opposite.
C)The force of your hand on the racket and the force of the racket on the ball are equal and opposite.
D)The force of the racket on your hand and the force of the racket on the ball are equal and opposite.
E)The force of your hand on the racket and the force of the racket on your hand are equal and opposite.

Question 34

When an acrobat hangs motionless from a pair of rings:

A)she has no measurable weight.
B)her weight depends on the angles the ropes make with the ceiling.
C)her weight is reduced by the upward force the rings exert on her.
D)her weight is increased by the upward force the rings exert on her.
E)she exerts a gravitational force on the Earth that is equal to the sum of the forces the rings exert on her.

Question 35

An 8.0-kg object rests on the floor of an elevator which is accelerating downward at a rate of 1.3 m/s2. What is the magnitude of the force the object exerts on the floor of the elevator?

A)59 N
B)10 N
C)89 N
D)68 N
E)78 N

Question 36

In order to jump off the floor, the floor must exert a force on you:

A)in the direction of and equal to your weight.
B)opposite to and equal to your weight.
C)in the direction of and less than your weight.
D)opposite to and less than your weight.
E)opposite to and greater than your weight.

Question 37

Two bodies, A and B, collide as shown in Figures I and II below. Which statement is true?

A)They exert equal and opposite forces on each other in I but not in II.
B)They exert equal and opposite force on each other in II but not in I.
C)They exert equal and opposite force on each other in both I and II.
D)The forces are equal and opposite to each other in I, but only the components of the forces parallel to the velocities are equal in II.
E)The forces are equal and opposite in I, but only the components of the forces perpendicular to the velocities are equal in II

Question 38

You throw a ball up in the air and hold your hand under it to catch it when it comes down. The reason why the ball stops is because:

A)your hand is there: your hand exerts no force on the ball.
B)your hand exerts a force on the ball perpendicular to its velocity.
C)your hand exerts a force on the ball in the direction of its velocity.
D)your hand exerts a force on the ball in the direction opposite to its velocity.
E)your hand and the ball exert forces in the same direction on each other.

Question 39

Two identical springs with spring constant 50 N/m support a 5.0 N weight as in the picture below. What is the tension in spring A?

A)1.45 N
B)2.50 N
C)2.89 N
D)3.75 N
E)5.00 N

Question 40

Three boxes slide on a frictionless horizontal surface when pulled by a force of magnitude F. When we compare the tensions T1 and T2 with the force F, we find that

A)T1 = T2 = F.
B)T1 = F > T2.
C)F > T1 = T2.
D)F > T1 > T2.
E)F - T1 < T1 - T2.

Question 41

Given the equation $(2.00 \mathrm{~kg})\left(5.00 \frac{\mathrm{~m}}{\mathrm{~s}^{2}}\right)=20.00 \mathrm{~N}-10.00 \mathrm{~N}$ , which answer or answers provide(s) the best description of a possible physical situation?

A)A 20.00 N tension pulls a 2.00 kg mass. The 2.00 kg mass pulls another 2.00 kg mass.
B)A 20.00 N force pushes a 2.00 kg mass. The 2.00 kg mass pushes another 2.00 kg mass.
C)A 2.00 kg mass on a flat surface is acted on by gravity while another 2.00 kg mass sits on top of it.
D)All of the situations above are possible.
E)Only (a) and (b) above are possible.

Question 42

A high-diver of mass 70.0 kg jumps off a board 10.0 m above the water. If, two seconds after entering the water, his downward motion is stopped, what average upward force did the water exert on him?

Question 43

Two experiments are performed. In (A), an 18.0 N force pushes horizontally on a 2.00 kg block that then pushes on a 4.00 kg block. In (B), an 18.0 N force pushes on a 4.00 kg block that then pushes on a 2.00 kg block. Which statement is correct?

A)The acceleration is 3.00 m/s2 in both (A) and (B).
B)The acceleration is 4.50 m/s2 in both (A) and (B).
C)The acceleration is 6.00 m/s2 in both (A) and (B).
D)The acceleration is 9.00 m/s2 in both (A) and (B).
E)The 2.00 kg block has a 9.00 m/s2 acceleration. The 4.00 kg block has a 4.50 m/s2 acceleration.

Question 44

A wicket keeper arranges to catch a cricket ball dropped from a height 50 m above his glove. However, his friends substitute a soft 250 g red grapefruit, so that it will smash apart when he catches it. His glove stops the grapefruit in 0.010 s. What force does the glove exert on the grapefruit?

A)0.078 3 N
B)783 N
C)2450 N
D)24 500 N
E)78 300 N

Question 45

A 2000-kg sailboat heading out to sea through the Sydney heads experiences an eastward force of 3000 N by the ocean tide and a wind force against its sails of magnitude 6000 N directed toward the northwest (45 $\degree$ N of W). What is the magnitude and direction of the resultant acceleration?

Question 46

A student is sitting on the right side of a school bus when it makes a right turn. We know that the force of gravity acts downwards and a normal force from the seat acts upwards. If the student stays in place when the bus turns, we also know that there must be:

A)no other force on the student.
B)a force parallel to the seat directed forward on the student.
C)a force parallel to the seat directed to the left on the student.
D)a force parallel to the seat directed to the right on the student.
E)a force parallel to the seat in a direction between forward and left on the student.

Question 47

Which of the following is not a fundamental force?

A)the gravitational force
B)the electromagnetic force
C)the strong force
D)the force of forward motion also known as the inertial force
E)Choose this answer if two of the named forces are not fundamental.