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JAMB Physics 1981 Question 25

Question 25

Motion

The driver in a motor car, of which the total mass is 800 kg and which is travelling at 20 m s−1, suddenly observes a stationary dog in his path 50 m ahead. If the car brakes can exert a force of 2000 N, what will most likely happen?

  1. A.The car will be able to stop immediately the driver notices the dog
  2. B.The car will stop 30 m after hitting the dog
  3. C.The car will stop 20 m in front of the dog
  4. D.The driver will quickly reverse the car
  5. E.The car will stop 5 m beyond the dog.
Show the answer and explanation

Answer: B (The car will stop 30 m after hitting the dog)

Explanation

Deceleration a = 2000/800 = 2.5 m s−2. Stopping distance = v²/2a = 400/5 = 80 m, which is 30 m beyond the dog 50 m ahead.