Question

Velocity - time graph of a particle of mass $2\text{kg}$ moving in a straight line is as shown in figure. Work done by all the forces on the particle is

• A. $400\text{J}$
• B. $-400\text{J}$
• C. $-200\text{J}$
• D. $200\text{J}$

Answer 1

The correct option is B $-400\text{J}$

Given :

$m=2\text{kg}$

From the graph,

$v_i=20\text{m/s};v_f=0\text{m/s}$

Now applying work- energy theorem,

Work done by all forces $=$ change in kinetic energy

$W_{\text{all forces}}=\frac{1}{2}m(v_f^2-v_i^2)$

$\Rightarrow W_{\text{all forces}}=\frac{1}{2}\times 2\times (0-400)$

$\therefore W_{\text{all forces}}=-400\text{J}$

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

Key concept:- Work energy theorem - The theorem states that the work done by all the forces on a body is equal to the change in its kinetic energy.