Carlos is in an roof of a building of 20 meters tall, he throws a tennis ball vertically upwards at 15 m/s velocity after it reaches its highest height, the ball goes down until it reaches the ground (see the figure). Based on this information, answer the following.

Question

a) Time taken to reach the highest height
b) The highest height in relation to building base
c) Total flight time since the ball is thrown until it reaches the ground
d) Its velocity when it crashes to the ground

Answer 1

a. Vf = Vo + g*Tr = 0.
Tr = -Vo/g = -15/-9.8 = 1.53 s. = Rise time.

b. h1 = Vo*Tr + 0.5g*Tr^2 = Ht. above the roof. g = -9.8 m/s^2.

h = h1 + 20.

c. h = 0.5g*Tf^2.
h = h1 + 20.
g = 9.8 m/s^2.
Tf = Fall time.
Tf = ?

Tr + Tf = Total flight time.

d. Vf^2 = Vo^2 + 2g*h.
Vo = 0.
g = 9.8 m/s^2.
h = h1 + 20.