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A rigid rod of length 2 L is acted upon ...

A rigid rod of length `2 L` is acted upon by some forces. All forces labelled `F` have the same magnitude. Which cases have a non-zero net torque acting on the rod about its centre ?
.

A

I and II only

B

II and III only

C

I and III only

D

The net torque is zero in all cases.

Text Solution

Verified by Experts

The correct Answer is:
a
By sign convention anticlockwise moment (or torque) is taken as positive while clockwise moment (or torque) is taken as negative.
In cae I, net torque about its center is
`tau= F xx L + F xxL = 2FL`

In Case II, net torque about it center is
`tau=F xx L + F xx L/2 + F xx L = 5/2 FL`

In case III, net torque about its center is
`tau=-F xx L + F xx L/2- F xx L/2 + F xx L=0`
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