Question 1

Positive work can be done:

Accepted Answer

A) by friction on the tyres when a car is accelerating without skidding. 
B) by a spring when it launches a clown in the air. 
C) by a hand throwing a ball. 
D) by all of the above. 
E) only by (b) and (c) above.

Question 2

The only force acting on a 1.8-kg body as it moves along the x axis is given by Fx = -(3.0x) N, where x is in m. If the velocity of the body at x = 0 is vx = +8.0 m/s, at what value of x will the body have a velocity of +4.0 m/s?

Accepted Answer

A) 5.7 m 
B) 5.4 m 
C) 4.8 m 
D) 4.1 m 
E) 6.6 m

Question 3

A 2.0-kg block slides down a frictionless incline from point A to point B. A force (magnitude P = 3.0 N) acts on the block between A and B, as shown. Points A and B are 2.0 m apart. If the kinetic energy of the block at A is 10 J, what is the kinetic energy of the block at B?

Accepted Answer

A) 27 J 
B) 20 J 
C) 24 J 
D) 17 J 
E) 37 J

Question 4

A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm?

Accepted Answer

A) +2.0 J 
B) +20 J 
C) (-2.0 J) 
D) (-20 J) 
E) +40 J

Question 5

A 2.0-kg block situated on a frictionless incline is connected to a light spring (k = 100 N/m), as shown. The block is released from rest when the spring is unstretched. The pulley is frictionless and has negligible mass. What is the speed of the block when it has moved 0.20 m down the plane?

Accepted Answer

A) 76 cm/s 
B) 68 cm/s 
C) 60 cm/s 
D) 82 cm/s 
E) 57 cm/s

Question 6

If the resultant force acting on a 2.0-kg object is equal to $(3 \tilde{\mathbf{i}}+4 \tilde{\mathbf{j}})$ N, what is the change in kinetic energy as the object moves from $(7 \tilde{\mathbf{i}}-8 \tilde{\mathbf{j}})$ m to $(11 \tilde{\mathbf{i}}-5 \tilde{\mathbf{j}})$ m?

Accepted Answer

A) +36 J 
B) +28 J 
C) +32 J 
D) +24 J 
E) +60 J

Question 7

A 2.0-kg body moving along the x axis has a velocity vx = 5.0 m/s at x = 0. The only force acting on the object is given by Fx = (-4.0x) N, where x is in m. For what value of x will this object first come (momentarily) to rest?

Accepted Answer

A) 4.2 m 
B) 3.5 m 
C) 5.3 m 
D) 6.4 m 
E) 5.0 m

Question 8

A particle is subject to the potential $U=2 x^{2} y+6 y$ . What is the value of the y component of the force on the particle at the point (x, y) = (2.0, 3.0)?

Accepted Answer

A) 24 
B) (-24) 
C) 14 
D) (-14) 
E) 28

Question 9

The force of static friction exerted on an automobile's tyres by the ground:

Accepted Answer

A) provides the accelerating force that makes the car move forward. 
B) does positive work on the car while it is accelerating. 
C) does negative work on the car while it is decelerating. 
D) does everything listed in (a), (b) and (c). 
E) only does positive or negative work as in (b) or (c).

Question 10

Planets go around the sun in elliptical orbits. The highly exaggerated diagram below shows a portion of such an orbit and the force on the planet at one position along that orbit. The planet is moving to the right. F|| and $F_{\perp}$ are the components of the force parallel (tangential) and perpendicular (normal) to the orbit. The work they do is W|| and $W_{\perp}$ . At the position shown:

Accepted Answer

A) W|| slows the planet down; $W_{\perp}$ speeds it up. 
B) W|| slows the planet down; $W_{\perp}$ does no work on it. 
C) W|| speeds the planet up; $W_{\perp}$ does no work on it. 
D) W|| speeds the planet up; $W_{\perp}$ slows it down. 
E) W|| does no work on it; $W_{\perp}$ speeds the planet up.

Question 11

A group of rioting students throw rotten eggs at some passing politicians. Two eggs of equal mass are thrown with equal velocity. Egg B hits the soft padded shoulders of a politician's suit but egg A misses and hits the building wall behind them instead. Compare the work done on the eggs in reducing their velocities to zero.

Accepted Answer

A) More work was done on A than on B. 
B) More work was done on B than on A. 
C) The amount of work is the same for both. 
D) It is meaningless to compare the amount of work because the forces were so different. 
E) Work was done on B, but no work was done on A because the wall did not move.

Question 12

The graph below shows how the force on a 0.500 kg particle varies with position. If the particle has speed $v=2.23 \frac{\mathrm{~m}}{\mathrm{~s}}$ at x = 0.00 m, what is its speed in m/s when x = 8.00 m?

Accepted Answer

A) 2.00 
B) 10.7 
C) 14.8 
D) 15.0 
E) 21.1

Question 13

Two clowns are launched from the same spring-loaded circus cannon with the spring compressed the same distance each time. Clown A has a 40-kg mass; clown B a 60-kg mass. The relation between their kinetic energies at the instant of launch is:

Accepted Answer

A)  $K_{A}=\frac{3}{2} K_{B}$ . 
B)  $K_{A}=\sqrt{\frac{3}{2}} K_{B}$ . 
C) KA = KB. 
D)  $K_{B}=\sqrt{\frac{3}{2}} K_{A}$ . 
E)  $K_{B}=\frac{3}{2} K_{A}$ .

Question 14

Carts A and B have equal masses and travel equal distances on straight frictionless tracks while a constant force F is applied to A, and a constant force 2F is applied to B. The relative amounts of work done by the two forces are related by:

Accepted Answer

A) WA = 4 WB. 
B) WA = 2 WB. 
C) WA = WB. 
D) WB = 2 WA. 
E) WB = 4 WA.

Question 15

The work $\overrightarrow{\mathbf{F}}_{s p} \cdot d \overrightarrow{\mathbf{x}}$ done by the force exerted by the spring on a mass attached to the end of the spring when the mass has displacement d $\overrightarrow{\mathbf{x}}$ is

Accepted Answer

A) always negative. 
B) always positive. 
C) negative half the time, positive the other half of the time. 
D) positive more than it is negative. 
E) negative more than it is positive.

Question 16

A cricket ball is thrown and lands 120 m away. While the ball is in flight, assuming the effect of air friction is negligible, which of the following is true?

Accepted Answer

A) At maximum height the ball has its greatest kinetic energy. 
B) The horizontal component of the ball's kinetic energy is constant. 
C) The vertical component of the ball's kinetic energy is constant. 
D) The mechanical energy of the ball is greater when nearer to the ground. 
E) No answer above is correct.

Question 17

A force acting on an object moving along the x axis is given by Fx = (14x - 3.0x2) N where x is in m. How much work is done by this force as the object moves from x = -1 m to x = +2 m?

Accepted Answer

A) +12 J 
B) +28 J 
C) +40 J 
D) +42 J 
E) (-28 J)

Question 18

A 1.5-kg object moving along the x axis has a velocity of +4.0 m/s at x = 0. If the only force acting on this object is shown in the figure, what is the kinetic energy of the object at x = +3.0 m?

Accepted Answer

A) 18 J 
B) 21 J 
C) 23 J 
D) 26 J 
E) 8 J

Question 19

Two balls, A and B, of mass m and 2m respectively, are carried to height h at constant velocity, but B rises twice as fast as A. The work the gravitational force does on B is:

Accepted Answer

A) one quarter the work done on A. 
B) one half the work done on A. 
C) the same as the work done on A. 
D) twice the work done on A. 
E) four times the work done on A.

Question 20

Negative work can be done:

Accepted Answer

A) by friction on the tyres while a car is accelerating without skidding. 
B) by a spring at the bottom of an elevator shaft when it stops a falling elevator. 
C) by a hand catching a ball. 
D) by all of the above. 
E) only by (b) and (c) above.

Exam 6: Work, Force and Energy

Positive work can be done:

The only force acting on a 1.8-kg body as it moves along the x axis is given by Fx = -(3.0x) N, where x is in m. If the velocity of the body at x = 0 is vx = +8.0 m/s, at what value of x will the body have a velocity of +4.0 m/s?

A 2.0-kg block slides down a frictionless incline from point A to point B. A force (magnitude P = 3.0 N) acts on the block between A and B, as shown. Points A and B are 2.0 m apart. If the kinetic energy of the block at A is 10 J, what is the kinetic energy of the block at B?

A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm?

A 2.0-kg block situated on a frictionless incline is connected to a light spring (k = 100 N/m) , as shown. The block is released from rest when the spring is unstretched. The pulley is frictionless and has negligible mass. What is the speed of the block when it has moved 0.20 m down the plane?

If the resultant force acting on a 2.0-kg object is equal to $(3 \tilde{\mathbf{i}}+4 \tilde{\mathbf{j}})$ N, what is the change in kinetic energy as the object moves from $(7 \tilde{\mathbf{i}}-8 \tilde{\mathbf{j}})$ m to $(11 \tilde{\mathbf{i}}-5 \tilde{\mathbf{j}})$ m?

A 2.0-kg body moving along the x axis has a velocity vx = 5.0 m/s at x = 0. The only force acting on the object is given by Fx = (-4.0x) N, where x is in m. For what value of x will this object first come (momentarily) to rest?

A particle is subject to the potential $U=2 x^{2} y+6 y$ . What is the value of the y component of the force on the particle at the point (x, y) = (2.0, 3.0) ?

The force of static friction exerted on an automobile's tyres by the ground:

Two clowns are launched from the same spring-loaded circus cannon with the spring compressed the same distance each time. Clown A has a 40-kg mass; clown B a 60-kg mass. The relation between their kinetic energies at the instant of launch is:

Carts A and B have equal masses and travel equal distances on straight frictionless tracks while a constant force F is applied to A, and a constant force 2F is applied to B. The relative amounts of work done by the two forces are related by:

The work $\overrightarrow{\mathbf{F}}_{s p} \cdot d \overrightarrow{\mathbf{x}}$ done by the force exerted by the spring on a mass attached to the end of the spring when the mass has displacement d $\overrightarrow{\mathbf{x}}$ is

A cricket ball is thrown and lands 120 m away. While the ball is in flight, assuming the effect of air friction is negligible, which of the following is true?

A force acting on an object moving along the x axis is given by Fx = (14x - 3.0x2) N where x is in m. How much work is done by this force as the object moves from x = -1 m to x = +2 m?

A 1.5-kg object moving along the x axis has a velocity of +4.0 m/s at x = 0. If the only force acting on this object is shown in the figure, what is the kinetic energy of the object at x = +3.0 m?

Two balls, A and B, of mass m and 2m respectively, are carried to height h at constant velocity, but B rises twice as fast as A. The work the gravitational force does on B is:

Negative work can be done:

Exam 6: Work, Force and Energy

Positive work can be done:

The only force acting on a 1.8-kg body as it moves along the x axis is given by Fx = -(3.0x) N, where x is in m. If the velocity of the body at x = 0 is vx = +8.0 m/s, at what value of x will the body have a velocity of +4.0 m/s?

A 2.0-kg block slides down a frictionless incline from point A to point B. A force (magnitude P = 3.0 N) acts on the block between A and B, as shown. Points A and B are 2.0 m apart. If the kinetic energy of the block at A is 10 J, what is the kinetic energy of the block at B?

A 2.5-kg object falls vertically downward in a viscous medium at a constant speed of 2.5 m/s. How much work is done by the force the viscous medium exerts on the object as it falls 80 cm?

A 2.0-kg block situated on a frictionless incline is connected to a light spring (k = 100 N/m) , as shown. The block is released from rest when the spring is unstretched. The pulley is frictionless and has negligible mass. What is the speed of the block when it has moved 0.20 m down the plane?

A 2.0-kg body moving along the x axis has a velocity vx = 5.0 m/s at x = 0. The only force acting on the object is given by Fx = (-4.0x) N, where x is in m. For what value of x will this object first come (momentarily) to rest?

A particle is subject to the potential U=2x2y+6yU=2 x^{2} y+6 yU=2x2y+6y . What is the value of the y component of the force on the particle at the point (x, y) = (2.0, 3.0) ?

The force of static friction exerted on an automobile's tyres by the ground:

The graph below shows how the force on a 0.500 kg particle varies with position. If the particle has speed v=2.23 m sv=2.23 \frac{\mathrm{~m}}{\mathrm{~s}}v=2.23 s m​ at x = 0.00 m, what is its speed in m/s when x = 8.00 m?

Two clowns are launched from the same spring-loaded circus cannon with the spring compressed the same distance each time. Clown A has a 40-kg mass; clown B a 60-kg mass. The relation between their kinetic energies at the instant of launch is:

Carts A and B have equal masses and travel equal distances on straight frictionless tracks while a constant force F is applied to A, and a constant force 2F is applied to B. The relative amounts of work done by the two forces are related by:

The work F→sp⋅dx→\overrightarrow{\mathbf{F}}_{s p} \cdot d \overrightarrow{\mathbf{x}}Fsp​⋅dx done by the force exerted by the spring on a mass attached to the end of the spring when the mass has displacement d x→\overrightarrow{\mathbf{x}}x is

A cricket ball is thrown and lands 120 m away. While the ball is in flight, assuming the effect of air friction is negligible, which of the following is true?

A force acting on an object moving along the x axis is given by Fx = (14x - 3.0x2) N where x is in m. How much work is done by this force as the object moves from x = -1 m to x = +2 m?

A 1.5-kg object moving along the x axis has a velocity of +4.0 m/s at x = 0. If the only force acting on this object is shown in the figure, what is the kinetic energy of the object at x = +3.0 m?

Two balls, A and B, of mass m and 2m respectively, are carried to height h at constant velocity, but B rises twice as fast as A. The work the gravitational force does on B is:

Negative work can be done:

A particle is subject to the potential $U=2 x^{2} y+6 y$ . What is the value of the y component of the force on the particle at the point (x, y) = (2.0, 3.0) ?

The work $\overrightarrow{\mathbf{F}}_{s p} \cdot d \overrightarrow{\mathbf{x}}$ done by the force exerted by the spring on a mass attached to the end of the spring when the mass has displacement d $\overrightarrow{\mathbf{x}}$ is