Rotational Motion Question 82

Question: A rod of weight w is supported by two parallel knife edges A and B and is in equilibrium in a horizontal position. The knives are at a distance d from each other. The centre of mass of the rod is at distance x from A. The normal reaction on A is

Options:

A) wxd

B) wdx

C) w(dx)x

D) w(dx)d

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Answer:

Correct Answer: C

Solution:

  • As the weight w balances the normal reactions. So, w=N1+N2 …(i) Now balancing torque about the COM, i.e.

anti-clockwise momentum = clockwise momentum

N1x=N2(dx) Putting the value of N2 from Eq.

(i), we get N1x=(wN1)(dx)

N1x=wdwxN1d+N1x

N1d=w(dx)

N1=w(dx)d



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