Question

The coefficient of friction between two surfaces is $\mu =\mathrm{0.8.}$ The tension in the string as shown in the figure is

• A. $0N$
• B. $6N$
• C. $4N$
• D. $8N$

Answer 1

Answer: (A)

maximum friction force
$f_{max}=\mu N$
$=\mu mgcos30^{\circ }$
$=0.8\times 1\times 10\times \frac{\sqrt{3}}{2}$
$=4\sqrt{3}$
$=6.92N$
And $mgsin30^{\circ }=1\times 10\times \frac{1}{2}\text{ = }5N$
Also $T+f=mgsin30^{\circ }$
Since, the frictional force is more as compare to force $\left(mgsin30^{\circ }\right)$ i.e., $6.92N>5N.$
Therefore, the tension in the string would be zero. No motion will take place.