Vertical Acceleration in Space

Question

A girl throws a tennis ball vertically upward with an initial speed of 15.0 m/s from the surface of an atmosphere-free planet called Zork. 3 seconds later, the ball is moving upward with a speed of 8.0 m/s.

1. what is the acceleration due to gravity on the surface of this planet, Zork?
2. approximately how many seconds does it take for this tennis ball to reach its maximum height?
3. how high does the tennis ball rise?
4. determine the final velocity of the tennis ball when it returns to its original position.

Answer 1

Marissa-

v = u + at.

v = 8, u = 15, t = 3, giving a = -2.33 m/s² (so 2.33 m/s² downwards towards the planet)

At maximum height v = 0

0 = 15 - 2.33t, giving t = 6.44 s

s = ut + 0.5a t²

u = 15, t = 6.44, a = -2.33, giving s = 48.3 m

Assuming no air resistance, going to be the same as the initial speed, 15.0 m/s, downwards