A rifle bullet loses $$\left(\frac{1}{25}\right)$$th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is
A uniform chain has a mass m and length $$l$$. It is held on a frictionless table with one-sixth of its length hanging over the edge. The work done in just pulling the hanging part back on the table is
A sphere and a hollow cylinder without slipping, roll down two separate inclined planes A and B, respectively. They cover same distance in a given duration. If the angle of inclination of plane A is 30$$^\circ$$, then the angle of inclination of plane B must be (approximately)
Four spheres each of diameter $$2 a$$ and mass $$m$$ are placed in a way that their centers lie on the four corners of a square of side $$b$$. Moment of inertia of the system about an axis along one of the sides of the square is