Question 2
A fruit breaks off its stalk and falls vertically from rest, taking 4 s to reach the ground. What is its velocity at the moment it hits the ground? (g = 9.8 m s-2)
The right answer is the one marked above.
39.2 m s-1. Change in velocity = acceleration × time, and the initial velocity is 0:
velocity = 9.8 m s-2 × 4 s = 39.2 m s-1
Second by second it builds up like this: 0 as the fall begins; 9.8 after one second; 19.6 after two; 29.4 after three; and 39.2 m s-1 after four.
78.4 is the height fallen, in metres — not the velocity.