First slide

Thermal expansion

Question

A uniform metallic rod rotates about its perpendicular bisector with constant angular speed. If it is heated, uniformly to raise its temperature slightly

Easy

A

its speed of rotation increases
B

its KE of rotation decreases
C

its speed of rotation remains same
D

its speed increases because its moment of inertia increases.

Solution

As externl torque is zero, angular momentum (L) of the rod remains conserved. Now I = 1/12 ml² and KE = L²/2I
$\therefore KE \propto \frac{1}{{{l^2}}}$
Due to thermal expansion, l increases, so KE decreases.

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