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Quiz: Work, Energy, and Power

Test your understanding of work, energy, and power with these 10 questions.

1. What is the SI unit of work and energy?

  1. Newton
  2. Joule
  3. Watt
  4. Pascal
Show Answer

The correct answer is B. The SI unit of both work and energy is the Joule (J). One Joule equals one Newton-meter (1 J = 1 N·m). This comes from the definition of work: W = F·d, where force is in Newtons and distance is in meters.

Concept Tested: Work

See: Chapter 6 - Work, Energy, and Power

2. When you carry a heavy box horizontally across a room at constant velocity, how much work do you do against gravity?

  1. A large positive amount
  2. A small positive amount
  3. A negative amount
  4. Zero work
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The correct answer is D. Work is done only when force has a component in the direction of motion. When carrying a box horizontally, your upward force is perpendicular to the horizontal displacement. The angle between force and displacement is 90°, so W = F·d·cos(90°) = 0. You expend muscle energy, but no work is done against gravity.

Concept Tested: Work by Constant Force

See: Chapter 6 - Work, Energy, and Power

3. What is kinetic energy?

  1. The energy of motion
  2. The energy stored in stretched springs
  3. The energy due to an object's position
  4. The total mechanical energy of a system
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The correct answer is A. Kinetic energy is the energy possessed by an object due to its motion. It depends on the object's mass and the square of its velocity: KE = ½mv². A faster-moving object has more kinetic energy than a slower one with the same mass.

Concept Tested: Kinetic Energy

See: Chapter 6 - Work, Energy, and Power

4. A 2 kg ball falls from rest from a height of 5 m. What is its kinetic energy just before hitting the ground? (Use g = 10 m/s²)

  1. 10 J
  2. 50 J
  3. 100 J
  4. 20 J
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The correct answer is C. Using conservation of energy, the gravitational potential energy is converted to kinetic energy: PE = mgh = 2 × 10 × 5 = 100 J. When the ball reaches the ground, PE = 0 and KE = 100 J. Alternatively, find v using v² = 2gh = 2(10)(5) = 100, so v = 10 m/s, then KE = ½(2)(100) = 100 J.

Concept Tested: Gravitational Potential Energy

See: Chapter 6 - Work, Energy, and Power

5. What distinguishes conservative forces from non-conservative forces?

  1. Conservative forces are stronger than non-conservative forces
  2. Conservative forces allow energy to be recovered as work done by the object
  3. Conservative forces only exist in space
  4. Non-conservative forces follow Newton's laws while conservative forces do not
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The correct answer is B. For conservative forces (gravity, electric force, spring force), the work done depends only on initial and final positions, not on the path taken. Energy lost to a conservative force can be recovered. Non-conservative forces like friction dissipate energy as heat, making it unrecoverable.

Concept Tested: Conservative Forces

See: Chapter 6 - Work, Energy, and Power

6. A spring compressed by 0.1 m stores elastic potential energy. If you compress it by 0.2 m instead, how does the stored energy change?

  1. It doubles
  2. It quadruples
  3. It increases by 4 times
  4. It increases by 2 times
Show Answer

The correct answer is B. Elastic potential energy is given by PE = ½kx², where x is the compression/extension. Since energy depends on x², doubling the compression (0.1 m to 0.2 m) increases energy by a factor of 2² = 4. The energy quadruples.

Concept Tested: Elastic Potential Energy

See: Chapter 6 - Work, Energy, and Power

7. What does the work-energy theorem state?

  1. Work and energy are never equal
  2. The total work done on an object equals its change in kinetic energy
  3. Energy is always conserved in all systems
  4. Work is the same as power
Show Answer

The correct answer is B. The work-energy theorem states: W_net = ΔKE = KE_f - KE_i. This means the total work done by all forces equals the change in kinetic energy. It's a powerful tool for solving mechanics problems without needing to analyze acceleration directly.

Concept Tested: Work-Energy Theorem

See: Chapter 6 - Work, Energy, and Power

8. In a perfectly frictionless system, what can you conclude about mechanical energy?

  1. Mechanical energy increases continuously
  2. Mechanical energy is conserved and remains constant
  3. Mechanical energy decreases at a constant rate
  4. Mechanical energy is converted to chemical energy
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The correct answer is B. In a frictionless system, only conservative forces act. By conservation of energy, total mechanical energy (KE + PE) remains constant. Energy can transform between kinetic and potential forms, but the total amount stays the same.

Concept Tested: Conservation of Energy

See: Chapter 6 - Work, Energy, and Power

9. What is power in physics?

  1. The force applied to an object
  2. The rate at which work is done or energy is transferred
  3. The total energy of a system
  4. The resistance to motion
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The correct answer is B. Power is the rate at which work is done or energy is transferred. It's calculated as P = W/t (work divided by time) or P = F·v (force times velocity). The SI unit of power is the Watt (W), where 1 W = 1 J/s.

Concept Tested: Power

See: Chapter 6 - Work, Energy, and Power

10. Why are simple machines useful despite the principle of conservation of energy?

  1. They allow you to do more work with less energy input
  2. They let you apply less force, trading distance for effort
  3. They create energy from nothing
  4. They eliminate friction completely
Show Answer

The correct answer is B. Simple machines provide mechanical advantage by letting you apply less force to accomplish the same work, but you must apply that force over a greater distance. Energy is conserved: work_input = work_output. A 2:1 mechanical advantage means you use half the force but move twice the distance.

Concept Tested: Simple Machines

See: Chapter 6 - Work, Energy, and Power