A-level · Work, energy & power

PowerExam-style questions

Power as the rate of doing work, average power = work ÷ time, and the key working relationship P = Fv for a driving force — used to find engine power at constant speed and, by combining P = Fv with Newton's second law, the instantaneous acceleration of a vehicle on a level road or a hill.

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22 questions · A Level level · mark scheme and worked solution on each · no sign-up to try

DifficultyAllLevel 1Level 2Level 3Level 4Level 5
  1. 1
    A motorcycle and its rider have a combined mass of 250250 kg and are modelled as a particle.

    The motorcycle is being ridden down a straight road. The road slopes downwards at an angle α\alpha to the horizontal, where sin⁡α=125\sin\alpha = \frac{1}{25}

    The engine of the motorcycle works at a constant rate of 66 kW, and the non-gravitational resistance to the motion of the motorcycle is modelled as a constant force of magnitude 420420 N.

    Find the acceleration of the motorcycle at the instant when its speed is 12 m s−112\ \text{m s}^{-1}

    (5 marks)
    Level 3 · 5 marksTry it
  2. 2
    A car of mass 1000 kg1000\text{ kg} moves at a constant speed of 30 m s−130\text{ m s}^{-1} along a level road against a constant resistance of 600 N600\text{ N}. Find the power developed by the engine. (3 marks)
    Level 3 · 3 marksTry it
  3. 3
    A van's engine works at a constant 24 kW24\text{ kW} against a constant total resistance of 800 N800\text{ N} on a level road.

    Find the van's maximum speed. (3 marks)
    Level 3 · 3 marksTry it
  4. 4
    A pump raises 120 kg120\text{ kg} of water per minute through a vertical height of 8 m8\text{ m}, delivering it with negligible speed. Take g=10 m s−2g = 10\text{ m s}^{-2}.

    Find the average power of the pump. (4 marks)
    Level 3 · 4 marksTry it
  5. 5
    An electric motor working at a constant 2 kW2\text{ kW} raises a load of mass 50 kg50\text{ kg} vertically at constant speed. Take g=10 m s−2g = 10\text{ m s}^{-2}.
    (a) Find the speed of the load. (3 marks)
    (b) Find the time taken to raise the load through 24 m24\text{ m}. (1 mark)
    Level 3 · 4 marksTry it

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