A-level · Work, energy & power

Kinetic and potential energyExam-style questions

Kinetic energy ½mv² and gravitational potential energy mgh, the work–energy principle (the work done by the resultant force equals the change in kinetic energy), and conservation of mechanical energy — including motion along a smooth curved path, where only the overall energy change matters.

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

DifficultyAllLevel 1Level 3Level 4Level 5
  1. 1
    A child of mass 30 kg30\text{ kg} starts from rest at the top of a smooth curved slide and descends a vertical height of 5 m5\text{ m}. Taking g=10 m s−2g = 10\text{ m s}^{-2}:
    (a) Find the child's speed at the bottom of the slide. (3 marks)
    (b) Find the child's kinetic energy at the bottom. (2 marks)5 mv = ?
    Level 4 · 5 marksTry it
  2. 2
    A block of mass 3 kg3\text{ kg} is projected with speed 8 m s−18\text{ m s}^{-1} along a rough horizontal surface. A constant frictional force brings it to rest after a distance of 4 m4\text{ m}.
    (a) Find the initial kinetic energy of the block. (2 marks)
    (b) State the work done against friction. (1 mark)
    (c) Hence find the magnitude of the frictional force. (2 marks)
    Level 4 · 5 marksTry it
  3. 3
    A stone is thrown from ground level with speed 15 m s−115\text{ m s}^{-1}, in any direction. Air resistance is negligible; take g=10 m s−2g = 10\text{ m s}^{-2}.

    Use energy conservation to find its speed when it is 10 m10\text{ m} above the ground. (4 marks)
    Level 4 · 4 marksTry it
  4. 4
    A child of mass 45 kg45\text{ kg} descends a slide of vertical height 4 m4\text{ m}, starting from rest and arriving at the bottom moving at 6 m s−16\text{ m s}^{-1}. Take g=10 m s−2g = 10\text{ m s}^{-2}.

    Find the energy lost to resistive forces. (4 marks)
    Level 4 · 4 marksTry it
  5. 5
    A ball of mass 0.5 kg0.5\text{ kg} is dropped from rest at a height of 5 m5\text{ m} and rebounds to a height of 3.2 m3.2\text{ m}. Take g=10 m s−2g = 10\text{ m s}^{-2} and neglect air resistance.
    (a) Find the kinetic energy of the ball just before impact. (2 marks)
    (b) Find the energy lost in the bounce. (2 marks)
    (c) Find the rebound speed. (1 mark)
    Level 4 · 5 marksTry it