18. The centripetal force acting on a body rotating in a circle of radius ‘r’ is F. if the body moves in a circle of radius half of the initial value keeping other quantities const: then the %age changes in the centripetal force is :
13. A man has a mass of 80 kg. He ties himself with one side of the rope which passes over a single fixed pulley. He pulls on the other side of the rope to lift himself up at an average speed of 50 cm/s. what is the average useful power at which he is working?
4. Two boys weighting in the ratio of 4 : 5 goes up stair taking time in the ratio of 5:4.The ratio of their power is :
A bullet of mass m moving with velocity v is fired into a wooden block of mass M, If the bullet remains embedded in the block, the final velocity of the system is ____________.
49. the moon’s radius is 1.6× 106 m and the acceleration due to gravity g=1.6 ms-2 on its surface. find out the escape velocity from moon’s surface
