Question

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

• A. $400J$
• B. $-400J$
• C. $-200J$
• D. $200J$

Answer 1

The correct option is B $-400J$

From the graph we have

at t =0

Velocity of particle $\left(V_1\right)=20m{s}^{-1}$

$\Rightarrow K{E}_1=\frac{1}{2}m{v}_1^2=\frac{1}{2}\times 2\times 20\times 20$

$=400J$

Now,

at t = 2 sec.

Velocity of particle $\left(V_2\right)=0$

$\Rightarrow K{E}_2=0$

From, work - energy theorem

Work done by all forces (W) is equal to the change in kinetic enery $\left(\Delta KE\right)$ of the body.

i.e. $W=\Delta KE$

$\Rightarrow W=K{E}_2-K{E}_1$

$=0-400$

$\Rightarrow W=-400J$