WBJEE PYQs for Rotational Motion with Solutions: Practice WBJEE Previous Year Questions

1.

A mouse of mass m jumps on the outside edge of a rotating ceiling fan of the moment of inertia l and radius R. The frictionless loss of angular velocity of the fan as a result is, 

• \(\frac{mR^2}{1+mR^2}\)
• \(\frac{1}{1+mR^2}\)
• \(\frac{1-mR^2}{1}\)
• \(\frac{1-mR^2}{1+mR^2}\)

2.

A particle is moving in an elliptical orbit as shown in the figure. If $p$, $L$, and $r$ denote the linear momentum, angular momentum, and position vector of the particle (from focus $O$) respectively at a point $A$, then the direction of $\alpha = p \times L$ is along

• +ve x axis
• -ve x axis
• +ve y axis
• -ve y axis

3.

A small ball of mass m is suspended from the ceiling of a floor by a string of length L. The ball moves along a horizontal circle with constant angular velocity ω, as shown in the figure. The torque about the center (O) of the horizontal circle is:

• mgL sin θ
• mgL cos θ
• 0
• mgl cos θ

4.

The position vector of a particle of mass \(m\) moving with a constant velocity \(\mathbf{u}\) is given by \(\mathbf{r} = x(t)\hat{i} + b\hat{j}\), where \(b\) is a constant. At an instant, \(\mathbf{r}\) makes an angle \(\theta\) with the x-axis as shown in the figure. The variation of the angular momentum of the particle about the origin with \(\theta\) will be: