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Question
A boy travelling in an open car moving on a levelled road with constant speed tosses a ball vertically up in the air and catches it back. Sketch the motion of the ball as observed by a boy standing on the footpath. Give explanation to support your diagram.
Solution
Let the vertical velocity of the tossed ball be v and the speed of the car be u which must be equal to the horizontal velocity of the ball.
The ball has both components of motion, hence it will have a parabolic trajectory when observed from a distance. This can be shown in the figure below.
When this motion is observed by the boy sitting in the car, it will look like only a vertically up-down motion and he will catch the ball when it comes back to the ground if the car has a constant velocity.
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