Question 7
An object starting from rest is subjected to a uniform acceleration for 6 s and reaches a velocity of 12 m s-1. What is the object's displacement over that time?
The right answer is the one marked above.
36 m. Since the object moves with a uniform acceleration, the average velocity can be found by halving the sum of the initial and final velocities:
displacement = average velocity × time = (0 + 12) ÷ 2 × 6 s = 6 × 6 = 36 m
72 m is what you get by using the final velocity instead of the average — but the object was not travelling at 12 m s-1 for the whole time; it built up to it from 0.