Question

A body at rest has mass $10\text{kg}$. It is moved by a horizontal force of $5\text{N}$ on a frictionless horizontal surface. The work done by the force in $8\text{s}$ is -

• A. $\text{80 J}$
• B. $\text{85 J}$
• C. $\text{70 J}$
• D. $\text{60 J}$

Answer 1

The correct option is A $\text{80 J}$

Given:
$m=10\text{kg}$
$F=5\text{N}$
$t=8\text{s}$

So, acceleration,

$a=\frac{F}{m}=\frac{5}{10}=\frac{1}{2}{\text{m/s}}^2$

Displacement of body in $8\text{s}$,

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

$\Rightarrow s=0\times 8+\frac{1}{2}\times \frac{1}{2}\times 8^2$

$\Rightarrow s=16\text{m}$

Therefore, work done,

$W=Fs=5\times 16=80\text{J}$

​​​​​​​Hence, option $\left(A\right)$ is the correct answer.