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A ball is bouncing elastically with a sp...

A ball is bouncing elastically with a speed `1 m//s` between walls of a railway compartment of size `10 m` in a direction perpendicular to walls. The train is moving at a constant velocity of `10 m//s` parallel to the direction of motion of the ball. As seen from the ground, choose the correct option

A

the direciton of motion of the ball changes every 10 second .

B

speed of ball changes every 10 seconds

C

average speed of ball over any 20 second interval is fixed

D

the acceleration of ball is the same as from the train.

Text Solution

Verified by Experts

The correct Answer is:
(b,c,d)
The ball is moving with the moving train.So , the direction of motion of the ball is same as that of the train.
Speed of the ball as seen from the ground before collision with the wall on the other side of the train ` = 10 +1 = 11 m//s`.
Speed of the ball after elastic collision with the wall = 10 - 1 = 9 m/s.
The collision is prefectly elastic . So , momentum and kinetic energy are both conserved . So, average speed of the ball is over an interval of 20 sec is fixed . The velocity of train is constant `(=10 m//s)`. So, the ball is in interal frame and hene , the acceleraiton of the ball is teh same as from the train.
The correct options are (b), (c) and (d).
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