Question 4
The velocity of an object falls uniformly from 16 m s-1 to 4 m s-1 in 4 s. What is the object's retardation?
The right answer is the one marked above.
3 m s-2. Work out the acceleration first:
acceleration = (4 − 16) m s-1 ÷ 4 s = −3 m s-2
The value is negative, so this is a retardation, of magnitude 3 m s-2. That is, the velocity drops by 3 m s-1 every second: 16, 13, 10, 7, 4.
12 m s-2 is only the change in velocity — it still needs dividing by the time.