Question

A ball is thrown vertically upward and returns to its starting point 20 seconds later. Find its a) initial velocity; b) the maximum height it has reached.

 

Answer 1

Given:

$t=20\:\rm s$

The time of flight

$$t=\frac{2v_0}{g}$$

Hence,

a) initial velocity

$$v_0=gt/2=9.8*20/2=98\:\rm m/s$$

b) the maximum height that ball reached

$$h_{\max}=\frac{v_0^2}{2g}=\frac{98^2}{2*9.8}=490\:\rm m$$