# 546 - Physics Questions Answers

In a gravity free space a small ball is placed at the centre of a box of the same mass. The ball and the box both are moving with velocity u towards a fixed wall. Assume all collisions are perfectly elastic.

A) How many collisions are possible?

B) find velocities of the box and the ball and the position of the ball relative to the box after all possible collisions.

**Asked By: DIPYAMAN**

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. Dear Sir kindly help solve this question

**Asked By: RK GUPTA**

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A point source of light is placed at the centre of curvature

of a hemispherical surface. The radius of curvature is r

and the inner surface is completely reflecting. Find the

force on the hemisphere due to the light falling on it if

the source emits a power W.

**Asked By: ANKIT SHARMA**

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Dear Sir kindly help provide the correct approach and solution to solve this 2016 iit jee advanced rotational question.

For angular velocity about z axis there are two approaches in solutions available in books , internet , first one considering spin angular velocity and revolution angular velocity about z axis itself ; second one considering spin angular velocity and revolution angular velocity perpendicular to rod through O and then calculating angular velocity about z axis taking cosine component of revolution angular velocity.

May refer 2nd picture attached.

**Asked By: RK GUPTA**

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