An empty rail car of mass 100 kg is at rest railway track. A boy of mass 40 kg running speed of 5m/s jumps on the rail car. The speed (car + boy) system is how much?

A boy of mass 18 kg is running with a speed of 12 km/h. Find the kinetic energy possessed by the boy.

A shell of mass 0.020 kg is fired by a gun of mass 100 kg. If the muzzle speed of the shell is 80 m s^-1 , what is the recoil speed of the gun ?

A trolley of mass 200 kg moves with a uniform speed of 36 km//h on a frictionless track. A child of mass 20 kg runs on the trolley from one end to the other (10 m away) with a speed of 4 m s^-1 relative to the trolley in a direction opposite to the its motion, and jumps out of the trolley. What is the final speed of the trolley ? How much has the trolley moved from the time the child begins to run ?

What is the de-Broglie wavelength of a ball of mass 0.060 kg moving at a speed of 1.0 m/s.

A car is moving with a velocity of 54 kmh^-1 . What is the kinetic energy of a boy of mass 40 kg sitting in the car?

How much work is done on a body of mass 1 kg whirling on a circular path of radius 5m?

A constant retarding force of 50 N is applied to a body of mass 20 kg moving initially with a speed of 15m s^-1 . How long does the body take to stop ?