Tag: momentum

Quizzes (4) Questions (63)

Questions Related to momentum

Multiple choice modelling collisions collisions momentum work, energy and power physics

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 

  1. 1 : e

  2. e : 1
  3. $1 : e^3$
  4. $e^2 : 1 $
Reveal answer Fill a bubble to check yourself
D Correct answer
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$

Multiple choice modelling collisions collisions momentum work, energy and power physics

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 

  1. $30 ^ { \circ }$
  2. $60 ^ { \circ }$
  3. $90 ^ { \circ }$
  4. $120 ^ { \circ }$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

For a perfectly inelastic collision of equal masses m, m*v1 + m*v2 = 2*m*v_final. If v_final = v/2, then v1 + v2 = v. This implies the angle between the initial velocity vectors must be 90 degrees.

Multiple choice modelling collisions collisions momentum work, energy and power physics

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?

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Nothing is mentioned about coefficient of restitution. 

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