Question

39. A boy travelling in an open car moving on a levelled
road with constant speed of 4 m/s throws a ball with
the speed of u m/s, vertically up in the air with
respect to himself and catches it back. If speed of
the ball observed by a girl standing on footpath is
5 m/s, then angle of projection of the ball with the
horizontal as seen by the girl will be
(1) 37°
(2) 53°
(3) 30°
(4) 60°
​

Answer 1

Answer:

60 degree seen by the girl

Answer 2

With respect to the observer standing on the footpath ball is thrown with velocity u at an angle θ with the horizontal, hence it seems as a projectile. So path of the ball will be parabolic. The horizontal speed of the ball is same as that of the car, therefore, ball as well car travels equal horizontal ult distance. Due to its vertical speed, the ball follows a parabolic path.

Important point: We must be very clear that we are working with respect to ground. When we observe with respect to the car, motion will be along vertical direction only.

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