Physics · Science General

Collisions, Momentum and Kinetic Energy

331 Questions

Collisions, momentum, and kinetic energy questions analyze the principles of elastic and inelastic impacts. They require calculating mass, velocity, and conserved energy during physical interactions. These foundational physics topics are essential for most government engineering and general science examinations.

Elastic collisionsInelastic collisionsMomentum calculationKinetic energy principlesVelocity after impact

Collisions, Momentum and Kinetic Energy Questions

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A body of mass $M$ moving with a speed $u$ has a head-on collision with a body of mass $m$ originally at rest. If $M>>m$, the speed of the body of mass $m$ after collision will be nearly:

  1. $\dfrac{um}{M}$
  2. $\dfrac{uM}{m}$
  3. $\dfrac{u}{2}$
  4. $2u$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When a very massive body (M) hits a stationary light body (m) head-on, the light body is projected forward with twice the velocity of the massive body.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A ball moving with a certain velocity hits another identical ball at rest. If the plane is frictionless and collision is elastic, the angle between the directions in which the balls move after collision, will be

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

For an elastic collision between two identical masses where one is initially at rest, the angle between the final velocities is 90 degrees.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

Two perfectly elastic objects $A$ and $B$ of identical mass are moving with velocities $15\ m/s$ and $10\ m/s$ respectively collide along the direction of line joining them. Their velocities after collision are respectively:

  1. $10\ m/s, 15\ m/s$
  2. $20\ m/s, 5\ m/s$
  3. $0\ m/s, 25\ m/s$
  4. $5\ m/s, 20\ m/s$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$15m+10m=mv _1+mv _2$

$25=v _1+v _2$...............(i)
and $\dfrac{v _2-v _1}{u _1-u _2}=1$
$\Rightarrow \dfrac{v _2-v _1}{15-10}=1$
$\Rightarrow v _2-v _1=5$............(ii)
$v _1+v _2=25$
$\dfrac{v _2-v _1=5}{2v _2=30}$
$\therefore v _2=15m/s,v _1=10m/s$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A body of mass $8\ kg$ collides elastically with a stationary mass of $2\ kg$. If initial $KE$ of moving mass be $E$, the kinetic energy left with it after the collision will be:

  1. $0.80\ E$
  2. $0.64\ E$`
  3. $0.36\ E$
  4. $0.08\ E$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The fraction of kinetic energy retained by the incident mass m1 after an elastic collision with stationary mass m2 is ((m1 - m2)/(m1 + m2))^2. Here, m1=8, m2=2, so the fraction is ((8-2)/(8+2))^2 = (6/10)^2 = 0.36.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

If two bodies $A$ and $B$ of definite shape (dimensions of bodies are not ignored) $A$ is moving with speed of $10\ m/s$ and $B$ is in rest. They collide elastically. Then;

  1. body $A$ comes to rest and $B$ moves with speed of $10\ ms$

  2. they may move perpendicular to each other
  3. $A$ and $B$ may come to rest

  4. they must move perpendicular to each other
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In a general elastic collision between two bodies, the conservation of momentum and energy allows for various scattering angles depending on the impact parameter. They do not necessarily move perpendicular to each other unless the masses are equal and one is at rest.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A ball of mass $m$ moving with velocity $v$ collides elastically with another ball of identical mass coming from opposite direction with velocity $2v$. Their velocities after collision will be :

  1. $-v,2v$
  2. $-2v,v$
  3. $v,-2v$
  4. $2v,-v$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$mv-2mv=mv _{1}+mv _{2}$
$-v=v _{1}+v _{2}$...........(1)

and $\dfrac{v _{2}-v _{1}}{v+2v}=1\Rightarrow v _{2}-v _{1}=3v$............(2)
Solving eqs. $(i)$ and $(ii)$,
$v _{2}-v _{1}=3v$
$\dfrac{v _{2}+v _{1}=-v}{2v _{2}=2v}$
$\therefore v _{2}=v$ and $-v _{1}=2v\therefore v _{1}=-2v$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

Two solid rubber balls $A$ and $B$ having masses $200\ g$ and $400\ g$ respectively are moving in the opposite direction. A velocity of $A$ which is equal to $0.3\ m/s$. After the collision the two balls come to rest when the velocity of $B$ is 

  1. $0.15\ m/s$
  2. $1.5\ m/s$
  3. $-0.15\ m/s$
  4. $none\ of\ these$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

From conservation of linear momentum:

               $P _i=P _f$                  $(P _f=0)$

$m _{A}v _{A}+m _{B}v _{B}=0$
$v _{B}=-\dfrac{m _{A}v _{A}}{m _{B}}=-\dfrac{200\times 10^{-3}\times 0.3}{400\times 10^{-3}}$
$V _B=-\dfrac{60}{400}=-0.15$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A ball of mass m moving with velocity v collides elastically with another ball of identical mass coming from the opposite direction with velocity 2v. Their velocities after collision are :

  1. $-v,\:2v$
  2. $-2v,\:v$
  3. $v,\:-2v$
  4. $2v,\:-v$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When bodies of same mass collide head on elastically then after collision they exchange their velocities.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

A sphere $'P'$ of mass $'m'$ moving with velocity $'u'$ collides head-on with another sphere $'Q'$ of mass $'m'$ which is at rest. The ratio of final velocity of $'Q'$ to initial velocity of $'P'$ is
($e =$ coefficient of restitution)

  1. $\dfrac{e-1}{2}$
  2. ${\left[\dfrac{e+1}{2}\right]}^{{1}/{2}}$
  3. $\dfrac{e+1}{2}$
  4. ${\left[\dfrac{e+1}{2}\right]}^{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here,  ${m} _{1} = {m} _{2} = m$,     ${u} _{1} = u$,    ${u} _{2} = 0$
Let ${v} _{1},   {v} _{2}$ be their velocities after collision.
According to principle of conservation of linear momentum
$mu + 0 = m\left({v} _{1}+{v} _{2}\right)$
or   ${v} _{1} + {v} _{2} = v$       ....(i)
By definition,   $e = \dfrac{{v} _{2} - {v} _{1}}{u-0}$
or   ${v} _{2} - {v} _{1} = eu$      .....(ii)
Adding equations (i) and (ii), we get
${v} _{2} = \dfrac{u\left(1+e\right)}{2}    \Rightarrow    \dfrac{{v} _{2}}{u} = \dfrac{1+e}{2}$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

If two balls each of mass 0.06 kg moving in opposite directions with speed of $4\, m\, s^{-4}$ collide and rebound with same speed, then the impulse imparted to each ball due to other is:

  1. $0.48\, kg\, m\,s^{-1}$
  2. $0.53\, kg\, m\,s^{-1}$
  3. $0.8\, kg\, m\,s^{-1}$
  4. $0.92\, kg\, m\,s^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mass = $0.06kg$


Velocity= $4 m/s$

Rebound velocity = $-4 m/s$

Impulse = change in momentum 

Impulse = $m (u) – m (v)$

Impulse = $0.06 \times 4 – (0.06 \times -4) $

Impulse = $0.24 – (-0.24)$

Impulse = $0.24+0.24$


Impulse = $0.48kgm/s$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

 A ball of mass '$M$' moving with a velocity $\overrightarrow{V}$ collides head on elastically with another body of the same mass    '$M$' moving with a velocity $-\overrightarrow{V}$ in the opposite direction. After the collision :

  1. The velocities are exchanged by the two balls

  2. Both the balls come to rest

  3. Both of them move at right angles to the original line of motion
  4. One ball comes to rest and the other ball travels back with a velocity $2v$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since the collision is elastic, we know that when two bodies of same mass have an elastic collision their velocities get interchanged.
$m _1u _1+m _2u _2=m _1v _1+m _2v _2$


But $m _1=m _2=M,   u _1=V,   u _2=-V$

$\Rightarrow MV-MV=Mv _1+Mv _2$

$\Rightarrow v _1+v _2=0$.............(1)

The coefficient of restitution $(e)$ is given by,

$e=-\dfrac{v _1-v _2}{u _1-u _2}$


But for elastic collision,  $e=1$

$-\dfrac{v _1-v _2}{V+V}=1$

$\Rightarrow v _2-v _1=2V$..............(2)

From (1) and (2), we get,
$v _2=V$
$v _1=-V$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

 A heavy steel ball of mass greater than 1 kg moving with a speed of 2m/ s collides head on with a stationary ping pong ball of mass less than 0.1 g. The collision is elastic. After the collision the ping pong ball moves approximately with a speed

  1. $ 2 m / s $
  2. $4 m/ s$
  3. $2\times10^{4}m / s$
  4. $2\times10^{3}m / s$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Since the body is much heavy these won't be much change in velocity
& $e = 1$


i.e., $\dfrac{v-2}{0-2} = -1$

$\Rightarrow v = 4 m/s$

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

Consider the following statements A and B. Identify the correct choice in the given answer

 A : In a one - dimensional perfectly elastic collision between two moving bodies of equal masses, the  bodies merely exchange their velocities after collision

 B : If a lighter body at rest suffers perfectly elastic collision with a very heavy body moving with a certain velocity, after collision both travel with same velocity

  1. A and B are correct

  2. Both A and B are wrong

  3. A is correct B is wrong

  4. A is wrong B is correct
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A : Only possible case.
B : Since masses are not same velocities can't be same.

Multiple choice collisions in one dimension collisions work, energy and power mechanics physics

 Consider the following statements A and B and identify the correct answer:
$A :$ In an elastic collision, if a body suffers a head on collision with another of same mass at rest, the first body comes to rest while the other starts moving with the velocity of the first one.
$B :$ Two bodies of equal masses suffering a head-on elastic collision merely exchanges their velocities.

  1. A and B are true

  2. A and B are false

  3. A is true but B is false

  4. A is false but B is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For an elastic collision $($ using momentum conservation and coefficient of restitiution $)$,


$ v _1 = \dfrac{m _1-m _2}{m _1+m _2}u$

$ v _2 = \dfrac{2m _1}{m _1+m _2}u$.

If $m _1=m _2,$ then$, v _1 = 0 ,v _2 = u$.
In general, the velocities of the bodies just get interchanged in an elastic collision if their masses are equal.