Question 1Multiple choice · 1 markA* challenge
A 60 W lamp is switched on for 2.0 minutes.
How much energy is transferred?
- A 30 J
- B 120 J
- C 3600 J
- D 7200 J
Show answer
Answer: D
Free Energy, work & power questions for IGCSE Physics (0625), part of Motion, forces & energy. Each question has the answer and the marking points an examiner would look for.
Generate a full Energy, Work & Power worksheet →All Motion, forces & energy questionsA 60 W lamp is switched on for 2.0 minutes.
How much energy is transferred?
Answer: D
What is the unit of power?
Answer: C
An electric motor raises a lift of mass 750 kg through a height of 12 m at a steady speed in 30 s.
Calculate the increase in gravitational potential energy of the lift.
Use your answer to (a) to calculate the useful power output of the motor.
The electrical power input to the motor is 5000 W. Use your answer to (b) to calculate the efficiency of the motor.
State two forms of wasted energy in the motor.
State the principle of conservation of energy.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 88200 J ΔEp = mgΔh = 750 × 9.8 × 12 C1 88200 J A1 | 2 |
| (b) | 2940 W P = W/t = 88200/30 C1 2940 W A1 | 2 |
| (c) | 58.8% 2940/5000 × 100 C1 58.8% A1 | 2 |
| (d) | thermal energy (heating); sound internal / thermal energy in the motor and surroundings B1 sound B1 | 2 |
| (e) | energy cannot be created or destroyed, only transferred Any 1 of: energy cannot be created or destroyed; it is only transferred from one store to another B1 | 1 |
A student of mass 40 kg runs up a flight of stairs 3 m high in 5 s.
Calculate the gain in gravitational potential energy of the student.
Calculate the useful power developed.
State one other form of energy that the student’s chemical energy is transferred to.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | 1180 J ΔE = mgh = 40 × 9.8 × 3 C1 1180 J A1 | 2 |
| (b) | 235 W P = E ÷ t C1 235 W A1 | 2 |
| (c) | thermal (internal) energy thermal energy (internal energy of the body / surroundings) or kinetic energy B1 | 1 |
A roller-coaster car of mass 600 kg starts from rest at the top of a slope 35 m above the ground.
Describe the energy transfers as the car rolls down the slope.
Ignoring friction, calculate the speed of the car at ground level.
Calculate the speed of the car when it reaches the top of a second hill of height 15 m, ignoring friction.
Explain why the speed of the car does not depend on its mass.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | gravitational potential → kinetic, some to thermal (friction) gravitational potential energy decreases and kinetic energy increases B1 some energy is transferred to thermal energy / sound by friction and air resistance B1 | 2 |
| (b) | 26.2 m/s mgh = ½mv² C1 v = √(2 × 9.8 × 35) C1 26.2 m/s A1 | 3 |
| (c) | 19.8 m/s v = √(2 × 9.8 × 20) C1 19.8 m/s A1 | 2 |
| (d) | m cancels in mgh = ½mv² both kinetic energy and potential energy are proportional to mass, so mass cancels B1 | 1 |
Energy is stored and transferred in different ways.
Name the energy stores involved when a stretched catapult fires a stone upwards.
State the principle of conservation of energy.
| Part | Answer and marking points | Marks |
|---|---|---|
| (a) | elastic → kinetic → gravitational elastic (strain) energy B1 kinetic energy B1 gravitational potential energy B1 | 3 |
| (b) | energy cannot be created or destroyed energy cannot be created or destroyed, only transferred between stores B1 | 1 |
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