A rifle bullet loses `1/20th` of its velocity in passing through a plank. The least number of planks required just of stop the bullet is

solid sphere of mass 5 kg and radius 1 m is rotating about an axis passing through its centre. find constant tangential force required to rotate the sphere with 10 rad/s in two second . also find number of rotations completed by sphere in that time interval.

A bullet of mass 10 gm moving with a velocity 210 ms^(-I) is suddenly stopped. If its energy totally converted into heat,How much of heat in calories would be generated .

A body of mass 10 kg is moving wih a velocity of 100 cm s^-1 . Find the magnitude of force required to stop I in 10 second. How much distance will it move through before coming to rest ?