Question

A physics student drops a rock from a 55m cliff. How long does it take to hit the ground?

Answer 1

A physics student drops a rock from a 55 m cliff, it takes 3.35 seconds to hit the ground.

Solution:

Using the second equation of motion, $s=u t+\frac{1}{2} a t^{2}$

Where, U= initial velocity of ball

S = distance at which rock is dropped from cliff = 55 m

t = time period

a = acceleration due to gravity = 9.8 m/s

Since the ball is dropped from cliff, initial velocity is zero.

u = 0

$\begin{array}{l}{S=0 \times t+\frac{1}{2} 9.8 t^{2}} \\\\ {55=0+4.9 t^{2}} \\\\ {t^{2}=\frac{55}{4.9}=11.22} \\\\ {t=\sqrt{11.22} \approx 3.35 \text { second }}\end{array}$

Answer 2

Answer: 9.9 seconds

Explanation:

that's just how long it takes