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Inner and outer radii of a spool are r a...

Inner and outer radii of a spool are `r` and `R` respectively. A thread is wound over its inner surface and placed over a rough horizontal surface. Then:
.

A

Thread unwinds, spool rotates anticlockwise and friction acts leftwards

B

Thread winds, spool rotates clockwise and friction acts leftwards

C

Thread winds, spool moves to the right and friction act rightwards

D

Thread winds, spool moves to the right and friction does not come into existence

Text Solution

Verified by Experts

The correct Answer is:
B

For pure rolling point of contact must be the rest. `(a + R alpha = 0)` For that spool must rotate clock wise.
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