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Question:

A train is moving along a straight line with a constant acceleration a. A boy standing in the train throws a ball forward with a speed of 10 m/s, with respect to the train at an angle of 60° to the horizontal. The boy has to move forward by 1.15 m inside the train to catch the ball back at the initial height. The acceleration of the train, in m/s², is:

5

4

1

6

Solution:

Ball performs parabolic motion,
For vertical motion,s=ut - ½gt²
∴0=10sin60°t - ½×10×t²
∴t=√3s
For horizontal motion,s=ut+½at²
∴1.15=10cos60°×√3 + ½a(3)
∴a=5m/s²