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Energy

Science, Physics. Usually met in years 9 to 11.

Calculate gravitational potential energy, kinetic energy and efficiency, and link them in a falling object.

What you practise

Ends with the speed of a falling object from its height. Practice moves up a level when a round goes well and down when it does not.

Sample questions

Each sample comes with the method and the reason every wrong option is wrong. Real practice rounds are ten questions at your level.

Sample question, level 2 of 5

A 10 kg object moves at 5 m/s. What is its kinetic energy?

  1. 25 J
  2. 250 J
  3. 50 J
  4. 125 J
  5. 625 J
Show the answer and method

Answer: D, 125 J

The method: Kinetic energy = ½ × m × v² = ½ × 10 × 5² = ½ × 10 × 25 = 125 J.

Why the other options are wrong:

  • A, 25 J: The speed was not squared.
  • B, 250 J: The half was missed. Kinetic energy = ½ × mass × speed².
  • C, 50 J: The speed was doubled instead of squared.
  • E, 625 J: The whole of ½mv was squared, not just the speed.

Sample question, level 4 of 5

A 4 kg object has 200 J of kinetic energy. What is its speed?

  1. 25 m/s
  2. 7.071 m/s
  3. 50 m/s
  4. 100 m/s
  5. 10 m/s
Show the answer and method

Answer: E, 10 m/s

The method: Kinetic energy = ½mv², so v² = 2E ÷ m = 400 ÷ 4 = 100. Take the square root: v = 10 m/s.

Why the other options are wrong:

  • A, 25 m/s: The 2 went on the wrong side, and the square root was missed.
  • B, 7.071 m/s: The 2 was missed. v² = 2E ÷ m.
  • C, 50 m/s: This is energy ÷ mass. The speed comes from v² = 2E ÷ m, then a square root.
  • D, 100 m/s: The square root was not taken. This is v².

See where this fits: GCSE science with AQA and Key Stage 3.

Related topics: Density, Forces, Electricity, Waves.