Question

A ball is dropped from the difference of height 5m. Find the velocity with which it hits the ground.

• A. 10 m/s
• B. m/s
• C. 5 m/s
• D. - 10 m/s

Answer 1

The correct option is D

- 10 m/s

Since the ball is dropped

So u are initial velocity = 0

a = - 10 $m/s^2$ as in the negative y axis (remember the conventions)

s = - 5 m as the body is getting displaced in negative y-axis or down wards.

We need final velocity v

$v=u+at$ .....(1)

$s=ut+\frac{1}{2}a{t}^2$ ......(2)

$v^2=u^2+2as$ ..........(3)

We will need equation 3 "why” you ask

Because we know 3 of variables in equation 3 and need to find the fourth variable

$v^2=0^2+\alpha (-10)(-5)$

$v^2=100$

So, v =$\pm$10 which to pick we know when the particle hits the ground the find velocity is going to be in downward direction. So we choose v = - 10 m/s.