Question

A ball is thrown horizontality from a height of 20m and hits the ground with a speed that is three times it’s initial speed. What is the initial speed?

Answer 1

We have:

$$v_f^2=v^2+2gh$$

$$(3v)^2=v^2+2gh\to 8v^2=2gh$$

$$8v^2=2(9.8)(20)$$

$$v=7\frac{m}{s}$$