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CAIE A-Level Physics AS 5.1 Energy Conservation Questions

Practise connecting work, energy conservation, efficiency and power in mechanical calculations, including P = W/t and P = Fv.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • calculate work done from the component of force along displacement and use it in energy-transfer problems
  • apply conservation of energy to relate work, energy transfers and losses in mechanical systems
  • calculate efficiency and power from energy, work and time, including P = W/t and P = Fv

Covered syllabus points

5.1.1—The concept of work, and recall and use work done = force × displacement in5.1.2—The principle of conservation of energy5.1.3—That the efficiency of a system is the ratio of useful energy output5.1.4—The concept of efficiency to solve problems5.1.5—Power as work done per unit time5.1.6—P = W / t5.1.7—P = Fv and use it to solve problems

Question 1

[Maximum number: 1]

A box of weight 40 N is pushed with a horizontal force of 20 N along level ground for a distance of 2.4 m .

The box is then lifted at constant velocity through a height of 1.6 m by a vertical force.
What is the total work done on the box by the two forces?

A

80 J

B

110J

C

120 J

D

160 J

Question 2

[Maximum number: 1]

A block of mass 2.0 kg is released from rest on a slope. It travels 7.0 m down the slope and falls a vertical distance of 3.0 m . The block experiences a frictional force parallel to the slope of 5.0 N .

Figure for Question 2 — CAIE A-Level Physics AS

What is the speed of the block after falling this distance?

A

4.9 m s−14.9 \mathrm{~m} \mathrm{~s}^{-1}

B

6.6 m s−16.6 \mathrm{~m} \mathrm{~s}^{-1}

C

8.6 m s−18.6 \mathrm{~m} \mathrm{~s}^{-1}

D

10 m s−110 \mathrm{~m} \mathrm{~s}^{-1}

Question 3

[Maximum number: 1]

Which statement about efficiency is correct?

A

Efficiency does not have a unit.

B

The joule is a unit of efficiency.

C

The metre is a unit of efficiency.

D

The watt is a unit of efficiency.

Question 4

[Maximum number: 1]

In many filament lamps, as much as 92 J of energy is emitted as thermal energy for every 8 J of energy emitted as light.

What is the efficiency of a filament lamp, as the percentage of electrical energy converted to light energy?

A

8\%

B

9\%

C

91\%

D

92\%

Question 5

[Maximum number: 1]

Which expression could be used to calculate power?

A

( current )2 resistance \frac{(\text { current })^{2}}{\text { resistance }}

B

 force × displacement  time \frac{\text { force × displacement }}{\text { time }}

C

current × (resistance) 2{ }^{2}

D

 weight  time \frac{\text { weight }}{\text { time }}

Question 6

[Maximum number: 1]

A motor is used to lift a load vertically upwards.
The load has weight W.
The motor produces useful power output P.
The load is lifted at constant velocity v.
Which expression gives the time taken for the motor to lift the load vertically upwards through a distance d ?

A

PWd\frac{P}{W d}

B

WvP\frac{W_{v}}{P}

C

WdP\frac{W d}{P}

D

PvW\frac{P v}{W}

Question 7

[Maximum number: 1]

The force resisting the motion of a car is proportional to the square of the car's speed. The magnitude of the force at a speed of 20.0 m s−120.0 \mathrm{~m} \mathrm{~s}^{-1} is 800 N .

What useful output power is required from the car's engine to maintain a steady speed of 40.0 m s−140.0 \mathrm{~m} \mathrm{~s}^{-1} ?

A

32 kW

B

64 kW

C

128 kW

D

512 kW

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