2.6.3 Power and efficiency Quiz: Pearson Edexcel Physics, Unit 2

The 20 questions

1. Power is defined as:

   • The total energy transferred in one second.
   • The energy per unit mass.
   • The force divided by the velocity.
   • The rate of energy transfer, or the rate of work done.

2. The SI unit of power is the:

   • Joule (J)
   • Newton (N)
   • Joule per kilogram (J kg^-1)
   • Watt (W)

3. The efficiency of a device is defined as:

   • Useful energy output divided by total energy input.
   • Useful energy output multiplied by total energy input.
   • Total energy input divided by useful energy output.
   • Wasted energy divided by useful energy output.

4. A motor lifts a 50 kg load through 10 m in 5.0 s, at constant speed. What is the useful power output, taking g = 9.8 m s^-2?

   • 490 W
   • 980 W
   • 98 W
   • 9800 W

5. A motor has a power input of 1500 W and a power output of 1200 W. What is its efficiency?

   • 80%
   • 75%
   • 125%
   • 20%

6. A kettle has a power rating of 2000 W and is 80% efficient. What is its useful power output?

   • 400 W
   • 2000 W
   • 1600 W
   • 2500 W

7. A pump moves 1200 kg of water up 15 m in 60 s. What is the power needed to do this, taking g = 9.8 m s^-2?

   • 29 kW
   • 2.9 kW
   • 0.29 kW
   • 294 W

8. A device has an efficiency of 25% and a total power input of 800 W. What is its useful power output?

   • 3200 W
   • 25 W
   • 200 W
   • 800 W

9. An electric car applies a driving force of 500 N while moving at 20 m s^-1. What is the power output of the motor?

   • 25 kW
   • 500 W
   • 10 kW
   • 1 kW

10. A motor takes 240 W of input and raises a 10 kg mass at a steady 0.50 m s^-1. What is its efficiency, taking g = 9.8 m s^-2?

    • 4.9%
    • 80%
    • 49%
    • 20%

11. Machine X is 60% efficient with a power input of 1.0 kW. Machine Y is 40% efficient with a power input of 1.5 kW. Which statement is correct?

    • Neither machine has any useful output.
    • Machine X has the larger useful output.
    • Both have the same useful power output, 600 W.
    • Machine Y has the larger useful output.

12. A car moves at a constant 25 m s^-1 against a total resistive force of 800 N. What power must the engine deliver?

    • 32 kW
    • 20 kW
    • 800 W
    • 2 kW

13. Why can the efficiency of a device never exceed 100%?

    • Energy is conserved, so the useful output cannot be greater than the energy input.
    • Devices always waste more than they use.
    • Input energy is always less than output energy in a real device.
    • Efficiency is measured as a ratio of masses, not energies.

14. A lift of mass 500 kg rises at a constant 2.0 m s^-1. What is the power needed, taking g = 9.8 m s^-2?

    • 98 kW
    • 9.8 kW
    • 1.0 kW
    • 980 W

15. A 40 kW engine does 2.0 MJ of work. How long does this take?

    • 500 s
    • 0.02 s
    • 80 s
    • 50 s

16. A machine has a useful power output of 300 W and an efficiency of 60%. What is the total power input?

    • 500 W
    • 600 W
    • 180 W
    • 360 W

17. Which relationship gives the power of a force F acting on an object moving at constant velocity v in the direction of F?

    • P = F^2 v
    • P = Fv^2
    • P = F/v
    • P = Fv

18. A wind turbine's useful electrical output is 1.2 MW and its input power from the wind is 4.0 MW. What is its efficiency?

    • 80%
    • 120%
    • 3.3%
    • 30%

19. A cyclist produces 200 W of power and travels at constant speed, overcoming a 40 N resistive force. What is the cyclist's speed?

    • 5.0 m s^-1
    • 0.20 m s^-1
    • 8000 m s^-1
    • 40 m s^-1

20. A machine's total energy input is 2000 J and its wasted energy is 1700 J. What is its efficiency?

    • 1700%
    • 120%
    • 85%
    • 15%

Related quizzes

• Equations for uniformly accelerated motion Quiz · 2.1.1 · 20 questions
• Displacement, velocity and acceleration graphs Quiz · 2.1.2 · 20 questions
• Scalars, vectors and resolving and adding vectors Quiz · 2.2.1 · 20 questions
• Independence of projectile motion Quiz · 2.2.2 · 20 questions
• Free-body diagrams and Newton's first and second laws Quiz · 2.3.1 · 20 questions
• Weight, gravitational field strength and terminal velocity Quiz · 2.3.2 · 20 questions
• Newton's third law and momentum Quiz · 2.4.1 · 20 questions
• Conservation of linear momentum in one dimension Quiz · 2.4.2 · 20 questions
• Moments, centre of gravity and the principle of moments Quiz · 2.5.1 · 20 questions
• Work and kinetic energy Quiz · 2.6.1 · 20 questions