A roller coaster is designed such that riders experience ''weightlessness'' as they go round the top of a hill whose radius of curvature is 20 m. The speed of the car at the top of the hill is between

Sand is being dropped on a conveyer belt at the rate of M kg/s. The force necessary to keep the belt moving with a constant velocity of $$\upsilon $$ m/s will be :

A block B is pushed momentarily along a horizontaly surface with an initial velocity V. If  $$\mu $$  is the coefficient of sliding friction between B and the surface, block B will come to rest after a time

A block of mass m is placed on a smooth wedge of inclination $$\theta $$. The whole system is accelerated horizontally so that the block does not slip on the wedge. The force exerted by the wedge on the block will be (g is acceleration due to gravity)