Answer to Question #108085 in Mechanics | Relativity for Maro

Question

A ball is thrown straight up with a speed of 30 m/s.
(a.) How long does it take the ball to reach the maximum height?
(b.) What is the maximum height reached by the ball?
(c.) What is its speed after 4.2 s?

Answer 1

a)

$$t=\frac{v}{g}=\frac{30}{9.8}=3.1\ s$$

b)

$$h=\frac{v^2}{2g}=\frac{30^2}{2(9.8)}=46\ m$$

c) Velocity:

$$V=v-gT=30-(9.8)(4.2)=-11\frac{m}{s}$$

Negative sign means that a ball moves downwards.

Speed:

$$|V|=11\frac{m}{s}$$