IIT-JEE 2011 · Paper 2 · Physics Q33

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PhysicsInteger+4Question 33 of 60

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, 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

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Answer and worked solution

Official answer: 5

Train frame. The ball has $u_x=5$ m/s, $u_y=5\sqrt3$ m/s and a backward pseudo-acceleration $a$ .

Flight time $T=\dfrac{2u_y}g=\sqrt3$ s.

Displacement relative to the boy. $5\sqrt3-\frac12a(3)=1.15$ , so $8.66-1.5a=1.15$ and $a\approx5$ m/s².

Answer: 5

Topics:Pseudo forces and non-inertial frames Projectile motion

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IIT-JEE 2011 · Paper 2, Physics question 33