Question

The block starts from rest as shown in the figure. Find the work done by force of $10N$ and friction in the time $0$ to $4\sec$. [Take $g=10m/s^2$]

• A. 240 J ,-96 J
• B. 250 J , 96 J
• C. 240 J , 96 J
• D. 250 J ,-96 J

Answer 1

Answer: (A)

Here, applied force, $F=10N$

Friction force,
$f=\mu N=0.2\times mg=0.2\times 2\times 10=4N$
Net force, $F_{\text{net }}=F-f=10-4=6N$
$\therefore$ Acceleration, $a=\frac{F_{\text{net }}}{m}$
$=\frac{6}{2}=3m{s}^{-2}$
Distance covered in $4s$,
$s=0+\frac{1}{2}a{t}^2=\frac{1}{2}\times 3\times (4{)}^2=24m$
Work done by applied force of $10N$,
$W_1=Fs=10\times 24=240J$
Work done by friction force of $4N$,
$W_2=fs\cos 180^{\circ }=-4\times 24=-96J$