Question

 A rock is thrown horizontally from the top of a cliff 88 m high, with a horizontal speed of 25 m/s. For what interval of time is the rock in the air

Answer 1

$s=ut+ \frac{1}{2}at^2$

$88=0t+ \frac{1}{2} \times 9.8t^2$

$88= \frac{1}{2} \times 9.8t^2$

$88 \times 2 \times \frac{1}{9.8}= t^2$

$t=\sqrt{\frac{88 \times 2}{9.8}} =4.24 s$