Question

A body of mass$5kg$is dropped from a height of $1m$. Its kinetic energy just before reaching the ground is

• A. $49J$
• B. $98J$
• C. $168J$
• D. $28J$

Answer 1

The correct option is A

$49J$

Step 1: Given data

Mass of the body m$=5kg$

Height from which it is dropped h$=1m$

Step 2: To find kinetic energy just before reaching the ground.

As the body is dropped, its initial velocity u $=0m{s}^{-1}$

Let the velocity of the body just before reaching the ground be v.

From the equations of motion, we have

$v^2-u^2=2as$ Where, $a=9.8m{s}^{-2}$and s = height.

$v^2-0=2\times 9.8m{s}^{-2}\times 1m$

$v^2=19.6m{s}^{-2}$……..(1).

Kinetic energy $K.E=\frac{1}{2}m{v}^2$

$k.E=\frac{1}{2}\times g\times 19.6=49J$

Hence option A is correct.