Question 1

An object rests on an inclined surface. If the inclination of the surface is made steeper, what does the normal force on the object do?
A)increase
B)decrease
C)stays the same
D)The normal force is zero.
E)Cannot be determined without additional information.

Accepted Answer

As the inclination of the surface increases, the component of gravitational force perpendicular to the surface decreases, leading to a decrease in the normal force.

Question 2

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is
A)Mg.
B)Mg sin θ.
C)Mg cos θ.
D)Mg tan θ.
E)zero, since the plane is frictionless.

Accepted Answer

The normal reaction force exerted by the plane on the block is perpendicular to the plane, and therefore parallel to the x-y plane. By resolving the forces along the x-y plane, we get that the normal reaction force is equal and opposite to the y-component of the gravitational force, which is Mg cos θ. Therefore, the correct choice is C.

Question 3

A block is pushed up a 20.0° frictionless incline with an initial speed 12.0 m/s.
(a) How high up the plane does the block slide before coming to rest?
(b) How much time does it take to return to its starting position?

Accepted Answer

The answer of A block is pushed up a 20.0°...

Question 4

FIGURE 4-4 -Two masses, m₁ and m₂, are connected to each other as shown in Fig. 4-4. Mass m₁ slides without friction on the table surface. Both masses have acceleration of magnitude a as shown. How does the tension in the string compare to the weight, m₂g, of mass m₂? A)The tension is equal to m₂g. B)The tension is larger than m₂g. C)The tension is smaller than m₂g. D)It depends on m₁ being smaller than m₂. E)It depends on m₁ being larger than m₂.

Accepted Answer

The tension in the string is smaller than m₂g because m₂ is accelerating downward, meaning the net force on m₂ is m₂g - T = m₂a, where T is the tension.

Question 5

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.
A)It takes the lighter object 5 times longer to reach the bottom of the incline than the heavier.
B)It takes the lighter object 10 times longer to reach the bottom of the incline than the heavier.
C)It takes the heavier object 5 times longer to reach the bottom of the incline than the lighter.
D)It takes the heavier object 10 times longer to reach the bottom of the incline than the lighter.
E)The two objects reach the bottom of the incline at the same time.

Accepted Answer

The answer of Two objects have masses m and 5m,...

Question 6

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed
A)parallel to the plane in the same direction as the movement of the block.
B)parallel to the plane in the opposite direction as the movement of the block
C)perpendicular to the plane.
D)toward the center of the Earth.
E)an angle θ below the inclined plane.

Accepted Answer

The gravitational force always acts toward the center of the Earth, regardless of the orientation of the surface on which an object is moving.

Question 7

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is directed
A)parallel to the plane in the same direction as the movement of the block.
B)parallel to the plane in the opposite direction as the movement of the block
C)perpendicular to the plane.
D)toward the center of the Earth.
E)an angle θ above the inclined plane.

Accepted Answer

The normal reaction force is always perpendicular to the surface of contact, which in this case is the inclined plane.

Question 8

Two toy cars (16 kg and 2.0 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Make a statement which best describes their acceleration after being released.
A)The 16-kg car accelerates 8 times faster than the 2.0-kg car.
B)The 16-kg car accelerates 2 times faster than the 2.0-kg car.
C)The 2.0-kg car accelerates 8 times faster than the 16-kg car.
D)The 2.0-kg car accelerates 2 times faster than the 16-kg car.
E)Both cars accelerate at the same rate.

Accepted Answer

The acceleration of both cars is the same because acceleration due to gravity on an inclined plane is independent of mass.

Question 9

FIGURE 4-1 
-In Fig. 4-1 the scale at left is attached to the ceiling and a mass of 1.00 kg hangs from it. It reads 9.81 N. The identical scale at the right is connected by perfect strings passing over perfect pulleys to two 1.00 kg masses hanging vertically at the end of the strings. The scale at right reads
A)exactly 9.81 N.
B)more than 9.81 N, but not quite twice as much.
C)less than 9.81 N.
D)exactly 19.62 N.
E)more than 19.62 N.

Accepted Answer

The tension in each string is 9.81 N, so the scale at right reads 2(9.81 N) = 19.62 N.

Question 10

Which of the following free-body diagrams best represent the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with a downward acceleration less than g? F_fis the force of the floor on the person and F_gis the force of gravity on the person. A) B) C) D) E)

Accepted Answer

The answer of Which of the following free-body diagrams best...

Question 11

You ride on an elevator that is moving with constant upward acceleration while standing on a bathroom scale. The reading on the scale is
A)equal to your true weight, mg.
B)more than your true weight, mg.
C)less than your true weight, mg.
D)could be more or less than your true weight, mg, depending on the magnitude of the acceleration.

Accepted Answer

When the elevator accelerates upwards, the scale must exert an additional force to support both your weight and the force due to the acceleration. This results in a reading greater than your true weight.

Question 12

A block lies on a smooth inclined plane tilted at an angle of 35° to the horizontal.
(a) Draw the free-body diagram for the block.
(b) Determine the block's acceleration as it slides down the inclined plane.
(c) If the block started from rest 8.5 m up the incline from its base, determine the block's speed when it reaches the bottom of the incline.
(d) How long did it take the block to reach the bottom of the inclined plane?

Accepted Answer

The answer of A block lies on a smooth inclined...

Question 13

FIGURE 4-6 
-In the Atwood machine shown in Fig. 4-6, if M = 0.60 kg and m = 0.40 kg. Ignore friction and the mass of the pulley.
(a) Draw free-body diagrams for mass M and mass m.
(b) Calculate the magnitude of the acceleration of the system.
(c) Calculate the tension in the string.

Accepted Answer

The answer of FIGURE 4-6 
-In the Atwood machine shown...

Question 14

A block lies on a horizontal frictionless surface. A horizontal force of 100 N is applied to the block giving rise to an acceleration of 3 m/s². (a) Determine the mass of the block. (b) Calculate the distance the block will travel is the force is applied for 10 s. (c) Calculate the speed of the block after the force has been applied for 10 s.

Accepted Answer

The answer of A block lies on a horizontal frictionless...

Question 15

FIGURE 4-7 
-Two boxes are connected by a cord running over a pulley as shown in Fig. 4-7. Box I of mass 8.0 kg rest on the top of the table; the coefficient of kinetic friction between box I and the table is 0.10. Box II has a mass of 15.0 kg.
(a) Draw the free-body diagrams for the two boxes, identifying all of the forces acting on each of the masses.
(b) Calculate the acceleration of the system.
(c) Calculate the tension in the cord.

Accepted Answer

The answer of FIGURE 4-7 
-Two boxes are connected by...

Question 16

FIGURE 4-5 
-Two identical masses are attached by a light string that passes over a small pulley, as shown in Fig. 4-5. The table and the pulley are frictionless. The masses are moving
A)with an acceleration less than g.
B)at constant speed.
C)with an acceleration greater than g.
D)with an acceleration equal to g.
E)with an acceleration that cannot be determined without additional information.

Accepted Answer

The masses are moving with an acceleration less than g because the tension in the string provides an upward force that reduces the net force acting on each mass, resulting in an acceleration less than g.

Question 17

FIGURE 4-3 
-A 16-kg fish is weighed with two spring scales, each of negligible weight, as shown in Fig. 4-3. What will be the readings on the scales?
A)The bottom scale will read 16 kg, and the top scale will read zero.
B)The sum of the two readings will be 32 kg.
C)The top scale will read 16 kg, and the bottom scale will read zero.
D)Each scale will show a reading greater than zero and less than 16 kg, but the sum of the two readings will be 16 kg.
E)Each scale will read 8 kg.

Accepted Answer

The answer of FIGURE 4-3 
-A 16-kg fish is weighed...

Question 18

Which of the following free-body diagrams best represent the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with a constant velocity? F_fis the force of the floor on the person and F_gis the force of gravity on the person. A) B) C) D) E)

Accepted Answer

The answer of Which of the following free-body diagrams best...

Question 19

FIGURE 4-2 
-Compare the two situations shown in Fig. 4-2. On the left (A), James is holding the rope and keeping the bucket at rest. On the right (B), James ties the rope to the bucket so that it keeps the bucket at rest. In both cases the bucket contains the same quantity of water. In what case is the tension in the rope lower?
A)right
B)left
C)It is the same in both cases.
D)need more data to answer

Accepted Answer

When the rope is tied to the bucket (right), the tension in the rope is lower because the rope is not actively supporting the weight of the bucket and water; it is simply holding it in place.

Question 20

A student pulls a box of books on a smooth horizontal floor with a force of 100 N in a direction of 37.0° above the horizontal. The mass of the box and the books is 40.0 kg.
(a) Draw the free-body diagram for the box.
(b) Calculate the acceleration of the box.
(c) Calculate the normal force acting on the box.

Accepted Answer

The answer of A student pulls a box of books...

Quiz 4: Dynamics: Newtons Laws of Motion

An object rests on an inclined surface. If the inclination of the surface is made steeper, what does the normal force on the object do?

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is

A block is pushed up a 20.0° frictionless incline with an initial speed 12.0 m/s. (a) How high up the plane does the block slide before coming to rest? (b) How much time does it take to return to its starting position?

FIGURE 4-4 -Two masses, m1 and m2, are connected to each other as shown in Fig. 4-4. Mass m1 slides without friction on the table surface. Both masses have acceleration of magnitude a as shown. How does the tension in the string compare to the weight, m2 g, of mass m2?

Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is directed

Two toy cars (16 kg and 2.0 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Make a statement which best describes their acceleration after being released.

You ride on an elevator that is moving with constant upward acceleration while standing on a bathroom scale. The reading on the scale is

FIGURE 4-6 -In the Atwood machine shown in Fig. 4-6, if M = 0.60 kg and m = 0.40 kg. Ignore friction and the mass of the pulley. (a) Draw free-body diagrams for mass M and mass m. (b) Calculate the magnitude of the acceleration of the system. (c) Calculate the tension in the string.

FIGURE 4-5 -Two identical masses are attached by a light string that passes over a small pulley, as shown in Fig. 4-5. The table and the pulley are frictionless. The masses are moving

FIGURE 4-3 -A 16-kg fish is weighed with two spring scales, each of negligible weight, as shown in Fig. 4-3. What will be the readings on the scales?

Which of the following free-body diagrams best represent the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with a constant velocity? Ff is the force of the floor on the person and Fg is the force of gravity on the person.

FIGURE 4-4 -Two masses, m₁ and m₂, are connected to each other as shown in Fig. 4-4. Mass m₁ slides without friction on the table surface. Both masses have acceleration of magnitude a as shown. How does the tension in the string compare to the weight, m₂g, of mass m₂?

Which of the following free-body diagrams best represent the free-body diagram, with correct relative force magnitudes, of a person in an elevator that is traveling upward with a constant velocity? F_fis the force of the floor on the person and F_gis the force of gravity on the person.