Question

An object is dropped from 42m tall building. How long does It take to reach the ground?

Answer 1

Answer:

It takes 2.93 s for the object to reach ground from the height of 42 m.

Explanation:

Given:

Displacement of the object is, $d=-42\ m$

As it is dropped, initial velocity of the object is, $u=0$

Acceleration of the object is equal to acceleration due to gravity and is equal to, $a=g=-9.8\ m/s^2$

Now, using Newton's equation of motion and plugging in the values, we get:

$d=ut+\frac{1}{2}at^2\\-42=0+\frac{1}{2}(-9.8)t^2\\-42=-4.9t^2\\t^2=\frac{-42}{-4.9}\\t^2=8.571\\t=\sqrt{8.571}=2.93\ s$

So, it takes 2.93 s for the object to reach ground from the height of 42 m.