Torque of Internal Forces

Q. A string is wrapped around the rim of a wheel of moment of inertia $0.20kg-m^2$ and radius $20\text{cm}$. The wheel is free to rotate about its axis. Initially, the wheel is at rest. The string is now pulled by a force of $20\text{N}$. Find the angular velocity (rad/s) of the wheel after 5 seconds.

Q. A string is wrapped around the rim of a wheel of moment of inertia $0.20kg-m^2$ and radius $20\text{cm}$. The wheel is free to rotate about its axis. Initially, the wheel is at rest. The string is now pulled by a force of $20\text{N}$. Find the angular velocity (rad/s) of the wheel after 5 seconds.

Q. The net torque produced by the internal forces is ___

1. Positive
2. Negative
3. Zero
4. Cannot Say

Q. A uniform bar of length $6a$ and mass $8m$ lies on a smooth horizontal table. Two point masses $m$ and $2m$, moving in the same horizontal plane with speeds $2v$ and $v$ respectively strike the bar (as shown in figure) and stick to the bar after collision. By denoting angular velocity (about centre of mass), total energy and velocity of centre of mass after collision as $\omega ,E$ and $v_o$ respectively, we can say that

1. $v_o=0$
2. $\omega =\frac{6v}{5a}$
3. $\omega =\frac{3v}{5a}$
4. $E=\frac{3}{5}m{v}^2$

Q. The net torque on a rigid body due to its internal forces is always zero.

1. True
2. False