Question

A ball at rest is dropped from the top of a mountain. What is the distance travelled by the ball in the first two seconds? ( Take acceleration due to gravity $g=9.8m{s}^{-2}$)

• A. $101.4m$
• B. $19.6m$
• C. $39.2m$
• D. $78.4m$

Answer 1

Answer: (B)

$19.6m$

Let downward direction be positive.
Given:
The ball is at rest initially. So, initial velocity is: $u=0$
Acceleration due to gravity: $g=+9.8m{s}^{-2}$
Time of travel, $t=2s$
Let the distance travelled by ball $s$.
From equation of motion,
$s=ut+\frac{1}{2}g{t}^2$
$s=0\times 2+\frac{1}{2}\times 9.8\times 2^2$
$s=19.6m$