Question

A $4kg$ block is attached to a vertical rod by means of two strings which are massless and inextensible. When the system rotates about the rod as axis, the strings become taut. The centripetal force acting on the mass $m$ is (given tension in the upper cord is $60N$).

• A. $80N$
• B. $63N$
• C. $43N$
• D. $53N$

Answer 1

Answer: (C)

$43N$

$mg+T_{2}cos\theta =T_{1}cos\theta$
$4\left(9.8\right)+T_2\times \frac{4}{5}=60\times \frac{4}{5}$
$T_2=11N$
Now the centripetal force acting is given as
$(T_1+T_2)\times sin\theta$
$(60+11)\times \frac{3}{5}$
=43