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AQA · GCSE · Physics · Higher

Initial velocity of the car calculation

Q05.1 4 marks
a=v−uta = \frac{v-u}{t}

At the start of the test the car was moving slowly.

Then the car accelerated at 5.8 m/s² for 2.5 s.

The final velocity of the car was 20 m/s.

Calculate the initial velocity of the car.

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Marking points

  1. 1 Uses acceleration = change in velocity/time with 5.8 m/s² and 2.5 s.
  2. 2 Rearranges to multiply acceleration by time.
  3. 3 Finds the change in velocity as 14.5 m/s.
  4. 4 Subtracts the change from the final velocity to obtain 5.5 m/s.

Full-mark answer

a = Δv/t, so Δv = at = 5.8 × 2.5 = 14.5 m/s. Initial velocity = final velocity − change in velocity = 20 − 14.5 = 5.5 m/s.

Why this answer loses marks

I added the velocity change to the final velocity.

The car sped up, so finding its earlier velocity requires subtracting the increase from the final velocity.

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