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AQA · GCSE · Physics · Higher

Its velocity at 40 km calculation

Q06.1 4 marks
v2−u2=2asv^2-u^2 = 2 a s

The rocket was initially stationary on the ground.

Then the rocket accelerated upwards until it reached a height of 40 km.

The constant acceleration of the rocket was 6.48 m/s².

Calculate the velocity of the rocket at a height of 40 km.

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Marking points

  1. 1 Converts 40 km to 40 000 m.
  2. 2 Uses v² − u² = 2as with u = 0, a = 6.48 m/s² and the height.
  3. 3 Takes the square root after evaluating v².
  4. 4 Obtains 720 m/s, with the official consequential allowances.

Full-mark answer

Convert the height: s = 40 km = 40 000 m. With u = 0, v² − u² = 2as gives v² = 2 × 6.48 × 40 000 = 518 400. Therefore v = √518 400 = 720 m/s.

Why this answer loses marks

I used the distance in kilometres in the equation.

The motion equation needs consistent SI units, so the height must first be converted to metres.

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