Section 3.10: Chapter 3 Test

Instructions: Answer all questions. Show full working for numerical problems. Calculators are allowed. Time allowed: 50 minutes.

Part A: Multiple Choice (10 × 2 = 20 marks)

  1. Work is defined as:
    1. Force × Mass
    2. Force × Displacement
    3. Force × Time
    4. Force × Acceleration

    Answer: (b) Force × Displacement

  2. The SI unit of energy is:
    1. Newton
    2. Joule
    3. Watt
    4. Pascal

    Answer: (b) Joule

  3. Which of the following is not a form of mechanical energy?
    1. Kinetic energy
    2. Potential energy
    3. Thermal energy
    4. Elastic energy

    Answer: (c) Thermal energy

  4. The rate at which work is done is called:
    1. Energy
    2. Power
    3. Efficiency
    4. Momentum

    Answer: (b) Power

  5. If a force is perpendicular to displacement, the work done is:
    1. Maximum
    2. Zero
    3. Negative
    4. Equal to Force

    Answer: (b) Zero

  6. Efficiency of a machine is defined as:
    1. \( \frac{W_{in}}{W_{out}} \times 100\%\)
    2. \( \frac{W_{out}}{W_{in}} \times 100\%\)
    3. \( \frac{P_{in}}{P_{out}} \times 100\%\)
    4. \( \frac{t}{W} \times 100\%\)

    Answer: (b)

  7. 1 horsepower (hp) is approximately equal to:
    1. 550 W
    2. 746 W
    3. 1000 W
    4. 1500 W

    Answer: (b) 746 W

  8. The work-energy theorem states:
    1. Work = Force × Time
    2. Work = Change in Kinetic Energy
    3. Work = Power × Velocity
    4. Work = Change in Potential Energy

    Answer: (b)

  9. Which of the following has the greatest kinetic energy?
    1. 2 kg moving at 3 m/s
    2. 1 kg moving at 6 m/s
    3. 3 kg moving at 2 m/s
    4. 5 kg moving at 1 m/s

    KE values: (a) 9 J, (b) 18 J, (c) 6 J, (d) 2.5 J. Answer: (b)

  10. If the efficiency of a machine is 80% and the input work is 500 J, the useful output is:
    1. 400 J
    2. 450 J
    3. 500 J
    4. 600 J

    Answer: (a) 400 J

Part B: Short Answer Problems (5 × 4 = 20 marks)

  1. A 50 N force is applied to push a box 4 m across a horizontal floor. Find the work done.
  2. A 2 kg mass moving at 5 m/s is brought to rest by a force in 0.5 s. Find the average power developed by the force.
  3. A motor lifts a 120 kg load to a height of 10 m in 20 s. Find the power output of the motor.
  4. A bow stores 60 J of potential energy when fully drawn. If all energy is transferred to a 0.05 kg arrow, find the speed of the arrow.
  5. A machine has an efficiency of 75%. If the useful work output is 300 J, calculate the input work required.

Part C: Long Answer Problems (2 × 10 = 20 marks)

  1. A 1500 kg car accelerates uniformly from rest to 20 m/s in 10 s. (a) Calculate the net work done on the car. (b) Find the average power developed. (c) If the engine’s efficiency is 30%, how much chemical energy is consumed?
  2. A 2 kg block slides down a frictionless incline of height 4 m. (a) Find its speed at the bottom. (b) If friction is present and 20 J of energy is lost as heat, what is the final speed of the block?
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