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Year 10 Science — Work, energy and power

Work out work done, kinetic energy, potential energy and power, say when work is positive, negative or zero, and explain what a pulley, a ramp and a lever actually change.

Name: ________________________

Before you start

The parts of a lever, each one named.

1234
  1. 1. The load, the weight to be lifted
  2. 2. The fulcrum, the fixed point the bar turns about
  3. 3. The effort, the push you apply
  4. 4. The load arm, from the load to the fulcrum

Put the fulcrum close to the load and the effort arm becomes long. A small push over a long distance then lifts a large load through a short one.

  1. 1.Put the working of a slingshot in order, starting from The elastic band is pulled back, and work is done on it.

    • The band is let go and pushes on the stone
    • The band returns to the shape it started in
    • The stone gains kinetic energy and shoots forward
    • The stretched band holds that work as stored energy
    • The elastic band is pulled back, and work is done on it

  2. 2.A machine raises a load of 300 N when an effort of 100 N is applied. What is its mechanical advantage? Answer with a number.

  3. 3.A book of mass 2 kg is raised 1.5 m above the floor. Taking g as 10 m/s², what is its potential energy, in J? Answer with a number.

  4. 4.Sort each case by the work the named force does on the named object.

    Groups: Positive work done on the object · Negative work done on the object · No work done on the object

    • A goalkeeper stopping a moving ball
    • A boy pushing a wheelchair forward
    • A girl slowly lowering a dumbbell
    • A person pushing hard on a rigid wall
    • Friction acting on a sliding stack of coins

  5. 5.A force of 25 N moves a crate 4 m along the direction of the force. How much work is done on the crate, in J? Answer with a number.

  6. 6.Three simple machines are sketched below. Tap the one that changes the direction of the force you apply without reducing how large it has to be.

    Write the number of the part.

    123

  7. 7.A ball of mass 0.2 kg moves at 30 m/s. What is its kinetic energy, in J? Answer with a number.

  8. 8.A student pushes as hard as she can against a rigid wall for a minute and gets tired. How much work has she done on the wall?

    • a) None, because the wall did not move
    • b) It cannot be worked out without knowing her mass
    • c) A small amount, because the wall moved a tiny distance
    • d) A large amount, because she applied a large force

Answer key — Year 10 Science — Work, energy and power

  1. 1. 1. The elastic band is pulled back, and work is done on it 2. The stretched band holds that work as stored energy 3. The band is let go and pushes on the stone 4. The stone gains kinetic energy and shoots forward 5. The band returns to the shape it started in
  2. 2. 3
  3. 3. 30
  4. 4. A boy pushing a wheelchair forward → Positive work done on the object; A goalkeeper stopping a moving ball → Negative work done on the object; Friction acting on a sliding stack of coins → Negative work done on the object; A girl slowly lowering a dumbbell → Negative work done on the object; A person pushing hard on a rigid wall → No work done on the object
  5. 5. 100
  6. 6. 1 — A wheel with a rope over it
  7. 7. 90
  8. 8. a) None, because the wall did not move