IB Diploma Programme (DP) - SL & HL · Physics

A.3 Work, energy and power: Practice Questions

5 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on A.3 Work, energy and power.

10 questions25 marksFree, no account

Question 1

1 mark

A particle has kinetic energy \(E_k\) when its speed is \(v\). What is the kinetic energy of the particle when its speed is increased to \(3v\)?

Question 2

1 mark

An object of mass \(m\) is pulled up a rough incline of vertical height \(h\) and slope length \(L\) at a constant speed. If the constant frictional force acting on the object is \(f\), what is the work done by the pulling force?

Question 3

1 mark

A motor pulls a block of mass \(m\) up a frictionless ramp inclined at an angle \(\theta\) to the horizontal. The block starts from rest and is pulled with a constant acceleration \(a\). What is the instantaneous power delivered by the motor at time \(t\)?

Question 4

1 mark

The unit of power, the Watt (W), can be expressed in terms of SI base units. Which of the following is correct?

Question 5

1 mark

A spring with spring constant \(k\) is compressed by a distance \(x\), storing elastic potential energy \(E_p\). If the spring is then compressed by a total distance of \(2x\), what is the new elastic potential energy stored in the spring?

Question 6

2 marks

A crate is pushed with a horizontal force of \(50\text{ N}\) across a floor for a distance of \(10\text{ m}\). Calculate the work done by this force.

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Question 7

4 marks

An electric motor with an efficiency of \(75\%\) lifts a mass of \(50\text{ kg}\) through a vertical height of \(12\text{ m}\) in \(10\text{ s}\). Calculate the electrical power input to the motor. (Use \(g = 9.8\text{ m s}^{-2}\)).

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Question 8

6 marks

A small block slides down a frictionless track from a height \(H\) and enters a vertical circular loop of radius \(R\). Determine the minimum height \(H\) required so that the block does not lose contact with the track at the top of the loop.

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Question 9

4 marks

An electric motor is used to raise a load of mass 50 kg vertically through a distance of 15 m in a time of 20 s. The load is moved at a constant speed.

(a) Calculate the gain in gravitational potential energy of the load.
(b) Determine the useful power output of the motor.
(c) The motor has an efficiency of 75%. Calculate the electrical power input to the motor.
(d) Calculate the total energy wasted as heat and sound during this process. (Use \( g = 9.81\text{ m s}^{-2} \))

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Question 10

4 marks

An electric motor is used to lift a load of \(250\text{ kg}\) vertically at a constant speed of \(1.2\text{ m s}^{-1}\). The motor has an efficiency of \(65\%\). (Use \(g = 9.81\text{ m s}^{-2}\)).
(a) Calculate the useful power output of the motor.
(b) Determine the electrical power input required by the motor.
(c) If the motor operates for \(20\text{ s}\), calculate the total energy dissipated to the surroundings as thermal energy and sound.

Write your answer out first, then check it against the worked solution.

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