Tag: momentum

Questions Related to momentum

A body dropped freely from a height h on to a horizontal plane, bounces up and down and finally comes to rest.The coefficient of restitution is e. The ratio of velocities at the beginning and after two rebounds is 

modelling collisions collisions momentum work, energy and power physics

  1. 1 : e

  2. e : 1

  3. $1 : e^3$

  4. $e^2 : 1 $

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Correct Option: D
Explanation:

Let initial velocity is v at time of collision. $v = \sqrt { 2gh } $

after first re bound velocity ${v} _{1} = ev$
after second rebound velocity ${v} _{2} = e{v} _{1} = {e}^{2}v$
ratio $=\dfrac { { v } _{ 2 } }{ v } =\dfrac { { e }^{ 2 }v }{ v } $
$ ={ e }^{ 2 }:1$

Two bodies of equal masses moving with equal speeds makes a perfectly inelastic collision. If the speed after the collision is reduced to half, the velocities of approach is 

modelling collisions collisions momentum work, energy and power physics

  1. $30 ^ { \circ }$

  2. $60 ^ { \circ }$

  3. $90 ^ { \circ }$

  4. $120 ^ { \circ }$

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Correct Option: C

Two small spheres of equal mass, and heading towards each other with equal speeds, undergo a headon collision (no external force acts on system of two spheres). Then which of the following statement is correct?

modelling collisions collisions momentum work, energy and power physics

  1. Their final velocities must be zero

  2. Their final velocities may be zero

  3. Each must have a final velocity equal to the others initial velocity

  4. Their velocities must be reduced in magnitude

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Correct Option: B
Explanation:

Nothing is mentioned about coefficient of restitution. 

Hence the only true statement is 'their final velocities may be zero.'