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Question
The torque of the weight of any body about any vertical axis is zero. If it always correct?
Solution
No, its not always correct.
Explanation: If the centre of mass of the body is not on the same vertical line as the normal reaction R of the body, a net torque acts on the body about its vertical axis. In fig. 1, R and CM lies in the same vertical line. Thus, there is no torque about any vertical axis
But in fig. 2, as R and CM do not lie along the same vertical line, there exists a torque about the vertical axis.
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