Question

A BALL IS RELEASED FROM HIGHT AND REBOUNDS WITH SAME SPEED AFTER HITTING THE GROUNDIF IT TRAVELS 20M IN FIRST 8 SECONDS FIND THE NOOF COLLISIONS MADE)

Answer 1

$(2N-1)t=8$ and $(2N-1)\frac{gt^2}{2}=20$

We have

$\frac{40}{2N-1}=g\frac{64}{(2N-1)^2} \to N=\frac{64}{80}g+0.5=$

$=\frac{64}{80}\cdot9.81+0.5 \approx8.$

So, $N=8$.