Deck 6: Work and Energy

Question 1

A donkey is attached by a rope to a wooden cart at an angle of 23^o to the horizontal. The tension in the rope is 210 N. If the cart is dragged horizontally along the floor with a constant speed of 6.0 km/h, calculate how much work the donkey does in 35 minutes.

A) 740 kJ
B) 290 kJ
C) 680 kJ
D) 11 kJ
E) 0.70 kJ

Answer 1

680 kJ

Question 2

A bullet with a mass of 12 g moving horizontally strikes a fixed, stationary block of wood and penetrates a distance of 5.2 cm. The speed of the bullet just before the collision is 640 m/s. Assuming the block remains stationary, magnitude of the average force that the wood exerted on the bullet was

A) 4.7 x 10⁴ N
B) 74 N
C) 4.7 x 10⁶ N
D) 7.4 x 10² N
E) 4.7 x 10⁵ N

Answer 2

4.7 x 10⁴ N

Question 3

Two parents moving into a new house attempt to pull a large crate down a large hallway. One parent applies a force of magnitude 150 N directed 45 degrees to the direction of motion, while the other parent applies a force of 120 N on the other side of the direction of motion. If they move the crate 15 m and perform work at 2.6 kJ, at what angle to the direction of motion did the second parent pull on the crate?

A) 54 degrees
B) 30 degrees
C) 60 degrees
D) 34 degrees
E) 56 degrees

Answer 3

56 degrees

Question 4

If mechanical work is done on a body, the body must

A) accelerate.
B) be in equilibrium.
C) not exert any force.
D) have no friction force exerted on it.
E) move.

Question 5

The work expended to accelerate a car from 0 to 30 m/s

A) is more than that required to accelerate it from 30 m/s to 60 m/s.
B) is equal to that required to accelerate it from 30 m/s to 60 m/s.
C) is less than that required to accelerate it from 30 m/s to 60 m/s.
D) can be any of the preceding, depending on the time taken.
E) is described by none of these statements.

Question 6

The weight of an object on the Moon is one-sixth its weight on Earth. A body moving with a given speed on the Moon has kinetic energy equal to ______________ it would have if it were moving at the same speed on Earth.

A) the kinetic energy
B) 1/36 the kinetic energy
C) 1/6 the kinetic energy
D) 6 times the kinetic energy
E) 36 times the kinetic energy

Question 7

Initially a body moves in one direction and has kinetic energy K. Then it moves in the opposite direction with three times its initial speed. What is the kinetic energy now?

A) K
B) 3K
C) -3K
D) 9K
E) -9K

Question 8

A constant force of 45 N directed at angle $\theta$ to the horizontal pulls a crate of weight 100 N from one end of a room to another a distance of 4.0 m. Given that the vertical component of the pulling force is 12 N, calculate the work done by the force in moving the crate.

A) 4.1 x 10² J
B) 4.8 x 10¹ J
C) 3.9 x 10² N/m
D) 1.7 x 10² J
E) 3.9 x 10³ J

Question 9

Negative work means

A) the kinetic energy of the object increases.
B) the applied force is variable.
C) the applied force is perpendicular to the displacement.
D) the angle between the displacement vector and force vector is larger than 90^o.
E) nothing; there is no such thing as negative work.

Question 10

A variable force is represented on an F-versus-x graph. Which of the following is the work done by this force?

A) the slope of the curve
B) the area bounded by the curve and the x axis
C) the area bounded by the curve and the F axis
D) the F value multiplied by the x value
E) the F value divided by the x value

Question 11

A light rope runs through two frictionless pulleys of negligible mass. A mass, m, is hung from one of the pulleys and a force, F, is applied to one end of the rope so that the mass moves at a constant speed. If the force is applied over a distance, d, the distance the mass moves is

A) 0
B) d
C) d
D) d
E) 2d

Question 12

A 5.0-kg object slides down a frictionless surface inclined at an angle of 30^o from the horizontal. The total distance moved by the object along the plane is 10 meters. The work done on the object by the normal force of the surface is:

A) 0 kJ
B) 0.50 kJ
C) 0.43 kJ
D) 0.58 kJ
E) 0.25 kJ

Question 13

The SI unit of energy can be expressed as

A) kg · m/s
B) kg · m/s²
C) m/kg · s)
D) kg · m · s²
E) kg · m² · s²

Question 14

Two forces, both of magnitude 12 N and directed 35 degrees on either side of the direction of motion, pull a crate 15 m. How much work is done by the forces in moving the crate?

A) 1.8 x 10² J
B) 1.5 x 10² J
C) 2.9 x 10² J
D) 3.6 x 10² J
E) 2.1 x10² J

Question 15

The average marathon runner can complete the 42.2-km distance of the marathon in 3 h and 30 min. If the runner's mass is 75.0 kg, what is the runner's average kinetic energy during the run?

A) 842 J
B) 5450 J
C) 251 J
D) 126 J
E) 421 J

Question 16

A body moves with decreasing speed. Which of the following statements is true?

A) The net work done on the body is positive, and the kinetic energy is increasing.
B) The net work done on the body is positive, and the kinetic energy is decreasing.
C) The net work done on the body is zero, and the kinetic energy is decreasing.
D) The net work done on the body is negative, and the kinetic energy is increasing.
E) The net work done on the body is negative, and the kinetic energy is decreasing.

Question 17

Two identical crates with 100 kg mass are being pushed up at a constant speed an inclined plane that is at the angle of 20 degrees above the horizontal. One plane is frictionless, while the coefficient of friction between the crate and the other incline is 0.20. What is the absolute difference in work needed to push the crate a distance of 2.0 m along each plane?

A) 670 N
B) 1040 N
C) no difference
D) 370 N
E) 134 N

Question 18

A particle that is subjected to a variable force travels a distance of 20 m in a straight line in the same direction as the force. Picture shows the force exerted on the particle as a function of the position: What was the total work done by this force during the full 20-m trip?

A) 15 J
B) 30 J
C) 45 J
D) 60 J
E) 75 J

Question 19

A light rope runs through two frictionless pulleys of negligible mass. A mass, m, is hung from one of the pulleys and a force, F, is applied to one end of the rope so that the mass moves at a constant speed. What is the force needed to move the mass at a constant speed?

A) 0
B) mg
C) Mg
D) 2mg
E) 4mg

Question 20

The kinetic energy of a car is 1.00 x 10⁵ J. If the car's speed is increased by 20 percent, the kinetic energy of the car becomes

A) 4.00 x 10³ J
B) 1.20 x 10⁵ J
C) 1.44 x 10⁵ J
D) 1.04 x 10⁵ J
E) 4.00 x 10⁵ J

Question 21

Two skiers start at the same place and finish at the same place. Skier A takes a straight, smooth route to the finish whereas Skier B takes a curvy, bumpy route to the finish. If you assume that friction is negligible, which of the following statements is true?

A) Skier A has the same speed as skier B at the finish.
B) Skier B has the greater speed at the finish.
C) Skier A has the greater speed at the finish because the route is straight.
D) Skier A has the greater speed at the finish because the route is smooth.
E) Skier A has the greater speed at the finish because the route is both straight and smooth.

Question 22

A vertical light spring stretches a distance h meters when a mass m is hung from it. The spring/mass system is now placed on a horizontal frictionless table and set into oscillation with amplitude h and maximum velocity v. What is the total energy of the the spring/mass oscillating system.

A) kh² +
Mv²
B) kh² + mgh
C) mv² +
Mgh²
D) mgh + kh² +
Mv²
E) mv²

Question 23

Which of the following statements is true?

A) The kinetic and potential energies of an object must always be positive quantities.
B) The kinetic and potential energies of an object must always be negative quantities.
C) Kinetic energy can be negative but potential energy cannot.
D) Potential energy can be negative but kinetic energy cannot.
E) None of these statements is true.

Question 24

In an old-fashioned television tube, an electron ) starting from rest experiences a force of 4.0 x 10^-15 N over a distance of 50 cm. Ignoring the relativistic effects, the final speed of the electron is:

A) 4.4 x 10¹⁵ m/s
B) 6.6 x 10⁷ m/s
C) 3.3 x 10⁷ m/s
D) 1.3 x 10⁸ m/s
E) 6.6 x 10⁸ m/s

Question 25

A block with a mass M = 4.85 kg is resting on a slide that has a curved surface. There is no friction. The speed of the block after it has slid along the slide sufficiently far for its vertical drop to be 19.6 m is

A) 19.6 m/s
B) 384 m/s
C) 73 m/s
D) 43.2 m/s
E) The problem cannot be solved because the shape of the curved slide is not given.

Question 26

A mass is attached to a spring with spring constant . The mass moves from position to position . The work done by the spring on the mass is:

A) 15.0 mJ
B) 0 J
C) -90.0 mJ
D) -15.0 mJ
E) 90.0 mJ

Question 27

A skier of mass 50 kg is moving at speed 10 m/s at point P₁ down a ski slope with negligible friction. What is the skier's kinetic energy when she is at point P₂, 20 m below P₁?

A) 2500 J
B) 9800 J
C) 12300 J
D) 13100 J
E) 15000 J

Question 28

The reference point for gravitational potential energy

A) must be at the initial position of the object.
B) must be at the final position of the object.
C) must be at ground level.
D) must be at the lowest position ever reached by the object.
E) can be chosen arbitrarily.

Question 29

The work-kinetic energy theorem states that

A) work done on an object is converted into kinetic energy and vice versa.
B) work done on an object comes from the kinetic energy.
C) work and kinetic energy are the same thing.
D) work and kinetic energy cannot co-exist at the same time.
E) none of the above

Question 30

The graph represents the force acting on a body plotted against the displacement of the body in the direction of the force. The total work done by the force from x = 0 to x = x is

A) m
B) mx² + b
C) · mx² + b
D) mx + b
E) · mx² + bx

Question 31

Kids love to crash their toy cars together. One such collision involves a 0.5 kg car moving at 0.3 m/s colliding with a stationary toy car of mass 0.3 kg. The two toys stick together and move away from the collision point at 0.188 m/s. What is the ratio of the initial kinetic energy of the system to the final energy of the system?

A) 0.63
B) 1.6
C) 2.5
D) 4.2
E) 1.0 The kinetic energy stays the same.)

Question 32

A car and its occupants, with a total mass m, are moving at a speed v relative to an observer on the side of the road. You are driving in another car, also traveling at speed v, and in the same direction as the first car. The kinetic energy of the first car relative to you is

A) 0
B) mv²
C) m2v)²
D) m 3v)²
E) depends on the mass of your car

Question 33

A mass m = 2.5 kg is sliding along a frictionless table with initial speed v as shown in the figure. It strikes a coiled spring that has a force constant k = 500 N/m and compresses it a distance x₂ - x₁ = -5.0 cm. The initial speed v of the block was

A) 0.71 m/s
B) 1.0 m/s
C) 1.4 m/s
D) 0.50 m/s
E) 1.7 m/s

Question 34

In pushing a load, a woman exerts a force as given by the graph. What was the total work done by the woman?

A) 400 J
B) 200 J
C) 2000 J
D) 1000 J
E) 500 J

Question 35

A motorcycle of mass m starting from rest can attain a speed v after work W is performed by its engine. If the engine could perform work 4W then the final speed would be?

A) 4v
B) 2v
C) 16v
D) 2v)^1/2
E) 4v)^1/2

Question 36

A force pushes a block along a horizontal surface against a force of friction . If the block undergoes a displacement at constant velocity, the work done by the resultant force on the block

A) is equal to the work done by the force of friction .
B) is given by .
C) increases the kinetic energy of the block.
D) increases the potential energy of the block.
E) is zero.

Question 37

You release an object from rest at a high altitude. If air resistance is considered, the curve that best represents the kinetic energy of the body as a function of the distance fallen is

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 38

Susana ascends a mountain via a short, steep trail. Sean ascends the same mountain via a long, gentle trail. Which of the following statements is true?

A) Susana gains more gravitational potential energy than Sean.
B) Susana gains less gravitational potential energy than Sean.
C) Susana gains the same gravitational potential energy as Sean.
D) To compare energies, we must know the height of the mountain.
E) To compare energies, we must know the lengths of the two trails.

Question 39

A woman runs up a flight of stairs. The gain in her gravitational potential energy is U. If she runs up the same stairs with twice the speed, what is her gain in potential energy?

A) U
B) 2U
C) U
D) 4U
E) U

Question 40

Car drag racing takes place over a distance of a mile 402 m) from a standing start. If a car mass 1500 kg) could be propelled forward with a pulling force equal to that of gravity, what would be the change in kinetic energy and the terminal speed of the car in mph) at the end of the race? For comparison, a modern, high-performance sports car may reach a terminal speed of just over 100 mph = 44.7 m/s.)

A) 604 kJ and 28.4 m/s
B) 5.92 kJ and 88.9 m/s
C) 5.92 MJ and 7900 m/s
D) 3680 kJ and 70.0 m/s
E) 5.92 MJ and 88.8 m/s

Question 41

A spring with force constant k = 300 N/m is compressed 9.0 cm. What is the potential energy in the spring?

A) 1.2 x 10⁴ J
B) 2.4 J
C) 2.7 x10⁴ J
D) 27 J
E) 1.2 J

Question 42

The total mechanical energy of any system is

A) always the work done by gravity.
B) the difference between the kinetic and potential energy at any point.
C) the sum of the kinetic and potential energy at any point.
D) the sum of the translational and rotational kinetic energies at any point.
E) the potential energy of a spring at any displacement.

Question 43

A 5200-kg cable car in Hong Kong is pulled a distance of 360 m up a hill inclined at 12^o from the horizontal. The change in the potential energy of the car is

A) 1.8 x 10⁷ J
B) 1.2 x10⁷ J
C) 3.8 x10⁶ J
D) 6.0 x10⁷ J
E) 1.8 x 10⁶ J

Question 44

Which of the following statements is NOT correct?

A) The work done by a conservative force on an object is independent on the path taken.
B) The work done by a conservative force on an object along path A $\rightarrow$ B is negative that of path B $\rightarrow$ A.
C) The force due to gravity is an example of a conservative force.
D) Friction is an example of a conservative force.
E) The work done by friction on an object depends on the path taken.

Question 45

A block of mass, m, is pushed up against a spring, compressing it a distance x, and is then released. The spring projects the block along a frictionless horizontal surface, giving the block a speed v. The same spring projects a second block of mass 4m, giving it a speed 3v. What distance was the spring compressed in the second case?

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

Question 46

A projectile of mass m is propelled from ground level with kinetic energy of 450 J. At the exact top of its trajectory, its kinetic energy is 250 J. To what height above the starting point does the projectile rise?

A) m
B) m
C) m
D) m
E) m

Question 47

The block shown in the figure is sliding on a frictionless surface. Its speed when it reaches the level portion of the surface on which it is sliding will be

A) 3.14 m/s
B) 7.67 m/s
C) 9.81 m/s
D) 13.3 m/s
E) 3.84 m/s

Question 48

According to quantum chromodynamics, the force that keeps quarks confined within a proton or neutron) increases as the separation between the individual quarks increases. Which statement below best represents this scenario?

A) The quarks are tied together by nonstretchable strings.
B) The quarks are tied together by elastic strings.
C) The quarks move independently of each other.
D) The force between the quarks has a 1/r² behavior like gravity.
E) The potential energy of a quark decreases with separation.

Question 49

A flexible rope of mass m and length L = L₁ + L₂, hangs over a frictionless peg, as shown in the figure. What is the speed of the rope when it just slides off the peg?

A)
B)
C)
D)
E)

Question 50

In magazine car tests an important indicator of performance is the zero to 60 mph 0 to 96.6 km/h) acceleration time. A time below 6.0 s is considered to be extremely quick. If a car with mass 1300 kg were dropped vertically from a great height, how long would it take to go from zero to 60 mph and what would the magnitude of the change in gravitational potential energy be during this time? neglect air resistance)

A) 2.74 s and 17.4 kJ
B) 2.74 s and 468 kJ
C) 2.74 s and 468 mJ
D) 0.37 s and 468 mJ
E) 2.74 s and 17.4 mJ

Question 51

A body falls through the atmosphere consider air resistance) gaining 20 J of kinetic energy. How much gravitational potential energy does it lose?

A) exactly 20 J
B) more than 20 J
C) less than 20 J
D) It is impossible to tell without knowing the mass of the body.
E) It is impossible to tell without knowing the displacement of the body

Question 52

A flexible rope of mass m and length L = L₁ + L₂, hangs over a frictionless peg, as shown in the figure. What is the change in potential energy when the end of the rope just slides off the peg?

A) mgL
B) mgL₁
C) mgL₂
D) mgL₁²/L)
E) mgL₁L₂/L)

Question 53

Two unequal masses hang from either end of a massless cord that passes over a frictionless pulley. Which of the following is true about the change in gravitational potential energy U) and the change in kinetic energy of the system K) after the masses are released from rest?

A) " $\Delta$ U < 0 and $\Delta$ K > 0"
B) " $\Delta$ U = 0 and $\Delta$ K > 0"
C) " $\Delta$ U < 0 and $\Delta$ K = 0"
D) " $\Delta$ U = 0 and $\Delta$ K = 0"
E) " $\Delta$ U > 0 and $\Delta$ K < 0"

Question 54

The graph shows a plot of the gravitational potential energy U of a 1.0-kg body as a function of its height h above the surface of a planet. The acceleration due to gravity at the surface of the planet is

A) 0.25 m/s²
B) 9.8 m/s²
C) 4.0 m/s²
D) 3.0 m/s²
E) 0.3 m/s²

Question 55

A woman on a bicycle traveling at 10 m/s on a horizontal road stops pedaling as she starts up a hill inclined at 3.0^o to the horizontal. If friction forces are ignored, how far up the hill does she travel before stopping?

A) 5.1 m
B) 30 m
C) 97 m
D) 10 m
E) The answer depends on the mass of the woman.

Question 56

The block shown in the figure is sliding on a frictionless surface before reaching the rough, leveled patch. If it takes the block 9.0 m to stop, what is the coefficient of kinetic friction between the block and the surface.

A) 3.14 m/s
B) 0.33
C) 0.66
D) 3.0
E) 3.3

Question 57

Which graphbest represents kinetic energy as a function of displacement from equilibrium for a mass attached to a spring displacing from to ?

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 58

A child is sitting on the seat of a swing with ropes 10 m long. Her father pulls the swing back until the ropes make a 37^o angle with the vertical and then releases the swing. If air resistance is neglected, what is the speed of the child at the bottom of the arc of the swing when the ropes are vertical?

A) 11 m/s
B) 8.8 m/s
C) 14 m/s
D) 6.3 m/s
E) 12 m/s

Question 59

Which graph best represents potential energy as a function displacement from equilibrium for a stretched spring?

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 60

A 75-kg man climbs the stairs to the fifth floor of a building, a total height of 16 m. His potential energy has increased by

A) 1.2 x 10⁴ J
B) 5.9 x10⁴ J
C) 4.7 x 10⁴ J
D) 3.8 x 10⁴ J
E) 5.9 x10³ J

Question 61

A 4.0-kg block starts from rest and slides 5.0 m down a plane inclined at 60^o to the horizontal. The coefficient of kinetic friction between the surface and the block is 0.20. The work done by friction on the block is

A) 98.0 J
B) 19.6 J
C) 3.92 J
D) 3.40 J
E) 64.0 J

Question 62

A mass m is released from a height h 60 cm from the right-hand side of the track shown in the diagram. There is only friction acting on the mass on the horizontal portion 35 cm either side of the midpoint O, with a kinetic coefficient of friction of $\mu$ _k = 0.50. What is the velocity of the block the first time it passes through the midpoint, and on which side of the midpoint does it stop?

A) 3.4 m/s, right
B) 3.9 m/s, right
C) 3.9 m/s, left
D) 2.9 m/s, left
E) 2.9 m/s, right

Question 63

A hanging block A m_A = 15 kg) is connected by a light cable and a pulley wheel to a second block B m_B = 10 kg) situated at the bottom of a frictionless inclined plane with angle 30 $\degree$ to the horizontal. If the hanging block is released from rest 5.0 m above the ground, find the maximum distance that block B travels up along the inclined plane.

A) 5.0 m
B) 4.0 m
C) 2.3 m
D) 7.3 m
E) 6.5 m

Question 64

A 5.0-kg box is pushed up with initial velocity and travels 5.0 m up a plane that is inclined at 30.0^o with the horizontal before it stops. The coefficient of kinetic friction between the box and the plane is 0.20. The initial velocity of the block is:

A) 5.8 m/s
B) 8.1 m/s
C) 4.0 m/s
D) 66 m/s
E) 16 m/s

Question 65

A system comprising two blocks is shown, one of which is on an inclined plane. The pulley is of negligible mass and is frictionless. The system starts from rest at position 1 and accelerates. Measurements taken when the blocks reach position 2 indicate that 1) the kinetic energy of block A has changed by 330 J;
2) the potential energy of block A has changed by 588 J;
3) the kinetic energy of block B has changed by 110 J; and
4) the potential energy of block B has changed by 98 J.The amount of mechanical energy that has been converted to heat because of friction is

A) 12 J
B) 50 J
C) 258 J
D) 478 J
E) 710 J

Question 66

Assuming the incline to be frictionless and the zero of gravitational potential energy to be at the elevation of the horizontal line,

A) the kinetic energy of the block just before it collides with the spring will be equal to mgh.
B) the kinetic energy of the block when it has fully compressed the spring will be equal to mgh.
C) the potential energy of the block when it has fully compressed the spring will be zero.
D) the energy stored in the spring plus the gravitational potential energy of the block when it has fully compressed the spring will be equal to mgh.
E) the potential energy of the block when it has fully compressed the spring will be

Question 67

A mass m is released from a height h 80 cm from the right-hand side of the track shown in the diagram at right. There is only friction acting along the horizontal portion 30 cm either side of the midpoint O with a kinetic coefficient of friction of $\mu$ _k = 0.4. Determine i) how many times does the mass m pass through the midpoint O, and ii) how far from the midpoint does it come to rest.

A) 6 and 0.1 m
B) 6 and 0.2 m
C) 3 and 0.2 m
D) 3 and 0.1 m
E) 1 and 0.02 m

Question 68

The surface shown in the figure is frictionless. The block is released from rest. What will be the maximum compression of the spring? Provide three significant digits in the final answer.)

A) 0.793 m
B) 3.24 m
C) 1.57m
D) 0.989 m
E) 0.886 m

Question 69

An object of mass m = 200 g slides down a frictionless ramp from a height H = 60 cm. Near the bottom of the ramp, the path changes into an arc of a circle with radius r = 20 cm. The arc has coefficient of kinetic friction $\mu$ _k = 0.4. The angle $\theta$ = 120 $\degree$ and points P₁ and P₂ which are the ends of the arc, are at the same height. What is the speed of the object at point P₁?

A) 1.1 m/s
B) 2.5 m/s
C) 3.1 m/s
D) 3.4 m/s
E) 4.1 m/s

Question 70

A 3.0-kg block sits on an incline where the top half of the incline has a coefficient of kinetic friction of 0.500 and the bottom half is frictionless. The angle of inclination is 35.0 degrees. If the block is released and travels 10.0 m along the rough part of the incline and then 10.0 m along the smooth part before it makes contact with the spring k = 200 N/m), calculate the distance the spring is compressed.

A) 1.47 m
B) 1.56 m
C) 2.16 m
D) 2.43 m
E) 1.39 m

Question 71

An object of mass m = 100 g slides down without rolling a rough incline from a height H = 60.0 cm. At h = 30.0 cm, the object flies off the incline. The coefficient of kinetic friction is 0.400, and the angle $\theta$ = 30.0 $\degree$ . How far from the base of the elevated incline does the object hit the floor?

A) 14.8 cm
B) 17.5 cm
C) 21.9 cm
D) 24.6 cm
E) 37.9 cm

Question 72

A 5.0-kg mass with initial velocity 20.0 m/s slides along a frictionless horizontal surface then up a frictionless ramp 2.0 m long and at an angle 30.0 degrees to the horizontal) and onto a second horizontal surface. The block slides over a rough surface 15.0 m in length $\mu$ _k = 0.400) before moving again on a frictionless surface and then impacting upon an uncompressed spring. If the block compresses the spring a distance 2.00 m, what is the spring constant k for the spring?

A) 304 N/m
B) 451 N/m
C) 84.0 N/m
D) 328 N/m
E) 353 N/m

Question 73

The work done by a conservative force between two points is

A) always positive.
B) always dependent upon the time.
C) always independent of the path.
D) zero.
E) never completely recoverable.

Question 74

A 10-kg box is pushed up a plane inclined at 37^o with the horizontal. The box starts from rest and is pushed 5.0 m along the incline with a uniform acceleration of 2.0 m/s². The coefficient of kinetic friction is 0.20 and the pushing force is parallel to the plane. The increase in the potential energy of the box is

A) 0.10 kJ
B) 0.29 kJ
C) 0.36 kJ
D) 0.46 kJ
E) 0.39 kJ

Question 75

A mass m is released from a height h 75 cm from the right-hand side of the track shown in the diagram. There is only friction acting on mass along the horizontal portion 30 cm either side of the midpoint O, with a kinetic coefficient of friction of $\mu$ _k = 0.40. Determine how high it reaches the second time it passes over to the left side, and in which direction is it moving when it stops?

A) 27 cm, right
B) 3.0 cm, right
C) 27 cm, left
D) 3.0 cm, left
E) 51 cm, right

Question 76

A 10-kg box is at the top of a 5.0-m plane inclined at 37^o with the horizontal. The box starts from rest and slides down the plane. The coefficient of kinetic friction is 0.20. The change in the potential energy of the box is

A) 0.08 kJ
B) 0.29 kJ
C) -0.29 kJ
D) -0.49 kJ
E) 0.49 kJ

Question 77

A 4.0-kg block starts from rest and slides 5.0 m down a plane inclined at 60^o to the horizontal. The coefficient of kinetic friction between the surface and the block is 0.20. The speed of the block after it slides 5.0 m is:

A) 2.2 m/s
B) 3.1 m/s
C) 0 m/s
D) 7.7 m/s
E) 6.3 m/s

Question 78

A 5.00-kg box is pushed 5.00 m up a plane that is inclined at 30.0^o with the horizontal. The coefficient of kinetic friction between the box and the plane is 0.200. The change in potential energy of the box is approximately

A) 12.5 J
B) 34.2 J
C) 123 J
D) 345 J
E) 403 J

Question 79

A 5.0-kg blob of putty is dropped from a height of 10.0 m above the ground onto a light vertical spring the top of which is 5.0 m above the ground. If the spring constant k = 200 N/m and the blob compresses the spring by 1.50 m, then find the amount of energy lost in sound and thermal energy.

A) 20.0 J
B) 169 J
C) 266 J
D) 438 J
E) 94.0 J

Question 80

Assuming the incline to be frictionless and the zero of gravitational potential energy to be at the elevation of the horizontal line,

A) the kinetic energy of the block just before it collides with the spring will be equal to mgh.
B) the kinetic energy of the block when it has fully compressed the spring will be equal to mgh.
C) the kinetic energy of the block when it has fully compressed the spring will be zero.
D) the kinetic energy of the block just before it collides with the spring will be kx².
E) the kinetic energy of the block when it has fully compressed the spring will be