Question

Velocity-time graph for a body of mass $10\text{kg}$ is shown in figure. Work done on the body in the first two seconds of motion is

• A. $12000\text{J}$
• B. $-12000\text{J}$
• C. $-4500\text{J}$
• D. $-9300\text{J}$

Answer 1

The correct option is C $-4500\text{J}$

Given,
$u=50\text{m/s}$
$v=0\text{m/s}$
$a=\frac{v-u}{t}=\frac{50}{10}=-5\text{m/s}$
$\therefore v=50-5t$

At $t=2\text{s},v_f=40\text{m/s},$
and at $t=0\text{s},v_i=50\text{m/s}$

According to Work Energy Theorem :
Work done in first 2 seconds
$W=\frac{1}{2}\left(10\right)\{v_f^2-v_i^2\}$
$W=\frac{1}{2}\times 10\{1600-2500\}=-4500\text{J}$