Question

Two blocks each of the mass `m` are attached to the ends, a massless rod which pivots as shown in figure. Initial the rod is held in the horizontal position and then release, Calculate the net torque on this system above pivot.

A. `(ml_(2)g-ml_(1)g)hatk`
B. `(ml1g-ml_(2)g)hatk`
C. `(ml_(1)g+ml_(2)g)hatk`
D. `-(ml1g+ml_(2)g)hatk`

Answer 1

Correct Answer - B
Torque due to weight of left `m`
`vectau_(1)=mgl_(1)hatk`(this is anticlockwise)
Torque due to weight of right `m`
`vectau_(2)=-mgl_(2)hatk`(this is clockwise)
So net torque `vectau=vectau+vectau_(2)=(mgl_(1)-mgl_(2))hatk`