Question

A rock is dropped from a 78-meter-high cliff. How long does it take to reach the ground?

Answer 1

Answer:

=20 m/s

The speed of stone when it hits the ground will be 20m/s.

Answer 2

Answer:

we have equation of motion

S = u×t + ½ a(t) ^2

were,

S - distance covered

u - initial velocity

t - time taken

a - acceleration

Here,

initial velocity is zero

u = 0

and acceleration is acceleration due to gravity. that is

a = g = 9.8 m/s^2

There for

S = u×t + ½ a(t) ^2

78 = 0×t + ½ × 9.8 × (t) ^2

78 = ½ × 9.8 × (t) ^2

78 × 2 = 9.8 × (t) ^2

156 = 9.8 × (t) ^2

t ^2 = 156 ÷ 9.8

= 15.91

t = 3.9887 s

~ 4 s