Question

A rod PQ of mass M and length L is hinged at end P. The rod is kept horizontal by a massless string tied to point Q as shown in figure. When string is cut, the initial angular acceleration of the rod is:

• A. $\frac{2g}{3L}$
• B. $\frac{3g}{2L}$
• C. $\frac gL$
• D. $\frac {2g} {L}$

Answer 1

Answer: (B)

$\frac{3g}{2L}$

Answer 2

$\tau = I \alpha$
$\Rightarrow mg \left( \frac{L}{2} \right) = \left( \frac{ml^2}{3} \right) \alpha$
$\Rightarrow \alpha = \frac{3g}{2L}$

So, the correct option is (B): $\frac{3g}{2L}$