Question

A force is applied on a body of mass $20\text{kg}$ moving with a velocity of $40\text{m/s}$. The body attains a velocity of $50\text{m/s}$ in $2\text{seconds}$. Calculate the work done by the body.

• A. $900\text{J}$
• B. $9000\text{J}$
• C. $18000\text{J}$
• D. $1800\text{J}$

Answer 1

The correct option is B $9000\text{J}$

We have the initial velocity $u=40\text{m/s}$ and final velocity $v=50\text{m/s}$

Using work energy theorem
Work done by the force$\left(W\right)$ $=$ Change in kinetic energy

$W=\frac{1}{2}m{v}^2-\frac{1}{2}m{u}^2$
$W=\frac{1}{2}\times 20({50}^2-{40}^2)$
$=10\times ({50}^2-{40}^2)$
$=10\times 900$
$W=9000\text{J}$

Hence option B is the correct answer