two balls of same size but of different material ,rubber and iron are kept on the smooth floor of a moving train.the brakes are applied suddenly to stop the train .Will the balls start rolling ?If so,in which direction ?Why they move with the same speed ?Give reasons for your answer .
The balls were moving when the train was moving. So when the train brakes are applied, the balls keep moving forward.
Exactly what does Newtons first law of motion state?
http://www.physicsclassroom.com/class/newtlaws/u2l1a.cfm
When the brakes are applied suddenly to stop the train, the train and everything inside it experiences a deceleration. This deceleration will cause the balls to move, but the direction and speed of their motion will depend on their material and the coefficient of friction between the balls and the smooth floor.
Since the balls are on a smooth floor, there will be no friction between the floor and the balls. However, there will be an additional force acting on the balls due to the deceleration of the train.
1. Rubber ball: The rubber ball will have a higher coefficient of restitution than the iron ball, meaning it is more elastic and has a better ability to regain its shape after being deformed. When the train decelerates, the rubber ball will slightly deform, absorbing some of the energy, and will eventually start rolling in the opposite direction of the train's motion. This is because the force exerted on the ball due to the deceleration will push it forward.
2. Iron ball: The iron ball, being a rigid and non-elastic material, will have less ability to absorb the energy of the deceleration. It will not deform significantly, and the force exerted on it due to the deceleration will push it forward in the opposite direction of the train's motion, causing it to roll.
Since both balls will experience the same deceleration force, they will start rolling with the same speed. However, the direction of their motion will be opposite to the direction of the train's motion.
In summary, both balls will start rolling in the opposite direction of the train's motion, but the rubber ball will slightly deform and absorb some energy, while the iron ball will remain rigid.