Question 1

State the Conservation of Mechanical Energy

Accepted Answer

In systems with cons

Question 2

An object of mass 20.0 kg is at rest at the top of an inclined plane whose length is 8.00 m and which makes an angle of 30.0° with the horizontal. The coefficient of kinetic friction between the object and the inclined plane is 0.400. The object is released and slides down the plane. What is the kinetic energy of this object at the bottom of the inclined plane? Use g = 10.0 m/s2.

Accepted Answer

A)  246 J 
B)  173 J 
C)  600 J 
D)  300 J 
E)  200 J 
A)  246 J 
B)  173 J 
C)  600 J 
D)  300 J 
E)  200 J

Question 3

FIGURE 8-4   An object of mass 2 kg is held at the top of a triangular wedge as shown in Figure 8-4, and then released. The reference level for potential energy is at the base of the triangle. Neglect friction and use g = 10 m/sS1U1P12S1S1P0.
-Refer to Figure 8-4. What is the gravitational potential energy of the object at the top of the wedge?

Accepted Answer

A)  30 J 
B)  40 J 
C)  100 J 
D)  60 J 
E)  80 J 
A)  30 J 
B)  40 J 
C)  100 J 
D)  60 J 
E)  80 J

Question 4

Describe the energy of a car driving up a hill.

Accepted Answer

A)  entirely kinetic 
B)  entirely potential 
C)  both kinetic and potential 
D)  gravitational 
E)  elastic 
A)  entirely kinetic 
B)  entirely potential 
C)  both kinetic and potential 
D)  gravitational 
E)  elastic

Question 5

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

Accepted Answer

A)  Work is + on the way up and + on the way down. 
B)  Work is + on the way up and - on the way down. 
C)  Work is - on the way up and + on the way down. 
D)  Work is - on the way up and - on the way down. 
A)  Work is + on the way up and + on the way down. 
B)  Work is + on the way up and - on the way down. 
C)  Work is - on the way up and + on the way down. 
D)  Work is - on the way up and - on the way down.

Question 6

A person drops a brick from the top of a building. The height of the building is 400 m and the mass of the brick is 2.00 kg. What will be the speed of the brick right before it touches the ground? Use g = 10.0 m/s2.

Accepted Answer

A)  10.0 m/s 
B)  13.2 m/s 
C)  89.4 m/s 
D)  59.4 m/s 
E)  63.2 m/s 
A)  10.0 m/s 
B)  13.2 m/s 
C)  89.4 m/s 
D)  59.4 m/s 
E)  63.2 m/s

Question 7

FIGURE 8-5   A 2.0-g bead slides along a wire, as shown in Figure 8-5. At point A, the bead is at rest. Neglect friction and use g = 10 m/sS1U1P12S1S1P0.
-Refer to Figure 8-5. What is the potential energy of the bead at point A?

Accepted Answer

A)  2.0 x 10-2 J 
B)  16 x 10-3 J 
C)  0.40 J 
D)  0 J 
E)  There is not enough information to solve this problem. 
A)  2.0 x 10-2 J 
B)  16 x 10-3 J 
C)  0.40 J 
D)  0 J 
E)  There is not enough information to solve this problem.

Question 8

An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U.

Accepted Answer

A)  K increases and U decreases. 
B)  K decreases and U decreases. 
C)  K increases and U increases. 
D)  K decreases and U increases. 
E)  Cannot be determined without knowing the initial height of the acorn. 
A)  K increases and U decreases. 
B)  K decreases and U decreases. 
C)  K increases and U increases. 
D)  K decreases and U increases. 
E)  Cannot be determined without knowing the initial height of the acorn.

Question 9

(a) A force of 15 N applied to a spring compresses it by 4 cm. What is the potential energy of the spring in the compressed position?
(b) A force of 15 N applied to a spring stretches it by 4 cm. What is the potential energy of the spring in the stretched position?

Accepted Answer

The answer of (a) A force of 15 N applied...

Question 10

A 20-kg object is resting at the top of a table 1.6 m above ground level. The object is then picked up and moved to a height of 8.7 m above ground level. What is the change in the gravitational potential energy of this object? Use g = 10 m/s2.

Accepted Answer

A)  71 J 
B)  140 J 
C)  1740 J 
D)  320 J 
E)  1420 J 
A)  71 J 
B)  140 J 
C)  1740 J 
D)  320 J 
E)  1420 J

Question 11

FIGURE 8-8  
-An object of mass 2.00 kg starts at rest from the top of a rough inclined plane of height 20.0 m as shown in Figure 8-8. If the work done by the force of friction is -150 J, what is the speed of the object as it reaches the bottom of the inclined plane? Use g = 10.0 m/s2.

Accepted Answer

A)  15.8 m/s 
B)  150 m/s 
C)  10.0 m/s 
D)  20.0 m/s 
E)  200 m/s 
A)  15.8 m/s 
B)  150 m/s 
C)  10.0 m/s 
D)  20.0 m/s 
E)  200 m/s

Question 12

FIGURE 8-3   A mass is attached to one end of a string. The other end of the string is attached to a rigid support. The mass is released at A and swings in a vertical arc to points B, C, and D, as shown in Figure 8-3. Neglect air resistance and use g = 10 m/   .
-Refer to Figure 8-3. At what point does the mass have the most kinetic energy?

Accepted Answer

A)  A 
B)  B 
C)  C 
D)  D 
E)  none of the given points 
A)  A 
B)  B 
C)  C 
D)  D 
E)  none of the given points

Question 13

An object of mass 2.00 kg is held at a position A, a vertical height of 20.0 m above the ground. Point B is 8.00 m directly below A. Neglect air resistance and use g = 10.0 m/s2.
(a) What is the speed of the object at position B when it falls from position A?
(b) What is the speed of the object just before it touches the ground?
(c) What is the ratio of the total energy of the object at position A to position B?

Accepted Answer

(a)12.6 m/

Question 14

FIGURE 8-11   A 2.0 kg mass is moving along the x-axis. The potential energy curve as a function of position is shown in Figure 8-11. The system is conservative. There is no friction.
-Refer to Figure 8-11. If the speed of the object at the origin is 4.0 m/s, what will be its speed at 7.0 m along the +x-axis?

Accepted Answer

A)  4.0 m/s 
B)  4.1 m/s 
C)  4.4 m/s 
D)  4.6 m/s 
E)  10 m/s 
A)  4.0 m/s 
B)  4.1 m/s 
C)  4.4 m/s 
D)  4.6 m/s 
E)  10 m/s

Question 15

An object of mass 20 kg is raised vertically through a distance of 8.0 m above ground level. Using g = 10 m/s2 what is the potential energy of this object at this position?

Accepted Answer

A)  1.6 J 
B)  16 J 
C)  160 J 
D)  1600 J 
E)  16000 J 
A)  1.6 J 
B)  16 J 
C)  160 J 
D)  1600 J 
E)  16000 J

Question 16

A 0.200-kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another 0.200-kg mass is added to the spring, the potential energy of the spring will be

Accepted Answer

A)  the same. 
B)  one-half as much. 
C)  twice as much. 
D)  3 times as much. 
E)  4 times as much. 
A)  the same. 
B)  one-half as much. 
C)  twice as much. 
D)  3 times as much. 
E)  4 times as much.

Question 17

An 8.0 kg object moving with an initial velocity of 8.0 m/s on a surface comes to rest due to friction after it travels a horizontal distance of 11 m. What is the coefficient of kinetic friction between the object and the surface? Use g = 10 m/s2.

Accepted Answer

A)  0.13 
B)  0.25 
C)  0.29 
D)  0.43 
E)  0.80 
A)  0.13 
B)  0.25 
C)  0.29 
D)  0.43 
E)  0.80

Question 18

The sum of the kinetic and potential energies of an object is conserved only when the object is under the influence of conservative forces.

Accepted Answer

A) True 
 B)False

Question 19

FIGURE 8-4   An object of mass 2 kg is held at the top of a triangular wedge as shown in Figure 8-4, and then released. The reference level for potential energy is at the base of the triangle. Neglect friction and use g = 10 m/sS1U1P12S1S1P0.
-Refer to Figure 8-4. What is the kinetic energy of the object at the top of the wedge?

Accepted Answer

A)  30 J 
B)  40 J 
C)  0 J 
D)  60 J 
E)  80 J 
A)  30 J 
B)  40 J 
C)  0 J 
D)  60 J 
E)  80 J

Question 20

FIGURE 8-6   A roller coaster of mass 80.0 kg is moving with a speed of 20.0 m/s at position A as shown in Figure 8-6. The vertical height at position A above ground level is 200 m. Neglect friction and use g = 10.0 m/sS1U1P12S1S1P0.
-What is the speed of the roller coaster at point C?

Accepted Answer

A)  0 m/s 
B)  34.6 m/s 
C)  69.2 m/s 
D)  20.0 m/s 
E)  There is not enough information to solve this problem. 
A)  0 m/s 
B)  34.6 m/s 
C)  69.2 m/s 
D)  20.0 m/s 
E)  There is not enough information to solve this problem.

Exam 8: Potential Energy and Conservation of Energy

State the Conservation of Mechanical Energy

Describe the energy of a car driving up a hill.

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

A person drops a brick from the top of a building. The height of the building is 400 m and the mass of the brick is 2.00 kg. What will be the speed of the brick right before it touches the ground? Use g = 10.0 m/s2.

FIGURE 8-5 A 2.0-g bead slides along a wire, as shown in Figure 8-5. At point A, the bead is at rest. Neglect friction and use g = 10 m/s2. -Refer to Figure 8-5. What is the potential energy of the bead at point A?

An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U.

(a) A force of 15 N applied to a spring compresses it by 4 cm. What is the potential energy of the spring in the compressed position? (b) A force of 15 N applied to a spring stretches it by 4 cm. What is the potential energy of the spring in the stretched position?

A 20-kg object is resting at the top of a table 1.6 m above ground level. The object is then picked up and moved to a height of 8.7 m above ground level. What is the change in the gravitational potential energy of this object? Use g = 10 m/s2.

FIGURE 8-8 -An object of mass 2.00 kg starts at rest from the top of a rough inclined plane of height 20.0 m as shown in Figure 8-8. If the work done by the force of friction is -150 J, what is the speed of the object as it reaches the bottom of the inclined plane? Use g = 10.0 m/s2.

An object of mass 20 kg is raised vertically through a distance of 8.0 m above ground level. Using g = 10 m/s2 what is the potential energy of this object at this position?

A 0.200-kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another 0.200-kg mass is added to the spring, the potential energy of the spring will be

An 8.0 kg object moving with an initial velocity of 8.0 m/s on a surface comes to rest due to friction after it travels a horizontal distance of 11 m. What is the coefficient of kinetic friction between the object and the surface? Use g = 10 m/s2.

The sum of the kinetic and potential energies of an object is conserved only when the object is under the influence of conservative forces.

FIGURE 8-6 A roller coaster of mass 80.0 kg is moving with a speed of 20.0 m/s at position A as shown in Figure 8-6. The vertical height at position A above ground level is 200 m. Neglect friction and use g = 10.0 m/s2. -What is the speed of the roller coaster at point C?

Introduction to Physics

One-Dimensional Kinematics

Vectors in Physics

Two-Dimensional Kinematics

Newtons Laws of Motion

Applications of Newtons Laws

Work and Kinetic Energy

Linear Momentum and Collisions

Rotational Kinematics and Energy

Rotational Dynamics and Static Equilibrium

Gravity

Oscillations About Equilibrium

Waves and Sound

Fluids

Temperature and Heat

Phases and Phase Changes

The Laws of Thermodynamics

Electric Charges, Forces, and Fields

Electric Potential and Electric Potential Energy

Electric Current and Direct-Current Circuits

Magnetism

Magnetic Flux and Faradays Law of Induction

Alternating-Current Circuits

Electromagnetic Waves

Geometrical Optics

Optical Instruments

Physical Optics: Interference and Diffraction

Relativity

Quantum Physics

Atomic Physics

Nuclear Physics and Nuclear Radiation

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A person drops a brick from the top of a building. The height of the building is 400 m and the mass of the brick is 2.00 kg. What will be the speed of the brick right before it touches the ground? Use g = 10.0 m/s².

FIGURE 8-5 A 2.0-g bead slides along a wire, as shown in Figure 8-5. At point A, the bead is at rest. Neglect friction and use g = 10 m/s². -Refer to Figure 8-5. What is the potential energy of the bead at point A?

A 20-kg object is resting at the top of a table 1.6 m above ground level. The object is then picked up and moved to a height of 8.7 m above ground level. What is the change in the gravitational potential energy of this object? Use g = 10 m/s².

FIGURE 8-8 -An object of mass 2.00 kg starts at rest from the top of a rough inclined plane of height 20.0 m as shown in Figure 8-8. If the work done by the force of friction is -150 J, what is the speed of the object as it reaches the bottom of the inclined plane? Use g = 10.0 m/s².

An object of mass 20 kg is raised vertically through a distance of 8.0 m above ground level. Using g = 10 m/s² what is the potential energy of this object at this position?

An 8.0 kg object moving with an initial velocity of 8.0 m/s on a surface comes to rest due to friction after it travels a horizontal distance of 11 m. What is the coefficient of kinetic friction between the object and the surface? Use g = 10 m/s².

FIGURE 8-6 A roller coaster of mass 80.0 kg is moving with a speed of 20.0 m/s at position A as shown in Figure 8-6. The vertical height at position A above ground level is 200 m. Neglect friction and use g = 10.0 m/s². -What is the speed of the roller coaster at point C?