Tag: introduction to momentum

Questions Related to introduction to momentum

The combined effect of mass and velocity is taken into account by a physical quantity called :

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. torque

  2. moment of force

  3. momentum

  4. moment of momentum

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Correct Option: C
Explanation:

Mass ad velocity both are considered to be quantities which defines motion.

The combination of both is called quantity of motion.
It is momentum.
$ P = mv$

A metallic ball strikes a wall and falls down whereas a tennis ball having the same mass and velocity bounces back. The conclusion from this is that :

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. Both suffer equal change in momentum

  2. The tennis ball suffers a greater change in momentum

  3. Metallic ball suffers a greater change in momentum

  4. The momentum of the tennis ball is less than that of the metallic ball

Show answer
Correct Option: B
Explanation:

For metallic ball,

$ \triangle P _M =0-mu=-mu$
For tennis ball,
$ \triangle P _T= -mu-mu = -2mu$
$ \therefore Option\ B\ is\ correct.$ 

Momentum is defined as :

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. weight

  2. mass

  3. mass$\times$velocity

  4. velocity

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Correct Option: C
Explanation:

Momentum is product of mass and velocity.

also known as "quantity of motion"'.

A ball comes back after an elastic collision with a wall, If initial momentum of the ball is P, the impulse on the wall after the collision is :

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. $P$

  2. $2P$

  3. $zero$

  4. $-2P$

Show answer
Correct Option: B
Explanation:

Initial momentum of the ball $=P$

 Final momentum of the ball $=-P$ 
Change in momentum $=-2P$
Impulse on the wall is equal to the change in momentum imparted on the wall $=2P$

A body of mass M collides with a wall with velocity V and rebounds with the same speed. Its change in momentum is equal to :

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. Zero

  2. MV

  3. 2MV

  4. 3MV

Show answer
Correct Option: C
Explanation:

$\Delta P={ P } _{ 1 }-{ P } _{ 2 }$ $[$ change in momentum$]$

$=MV-(-MV)\ \quad \quad \quad =-2MV$
negative sign denotes direction.
Hence option C is correct.

A disc of mass 10 g is kept floating horizontally by throwing 10 marbles per second against it from below. The marbles strike the disc normally and rebound downwards with the same speed. If the mass of each marble is 5 g, the velocity with which the marbles are striking the disc is $\displaystyle \left( g=9.8{ m }/{ { s }^{ 2 } } \right) $

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. $\displaystyle 0.98m/s$

  2. $\displaystyle 9.8m/s$

  3. $\displaystyle 1.96m/s$

  4. $\displaystyle 19.6m/s$

Show answer
Correct Option: A
Explanation:
Given that:
Mass of disc,$M=10g=0.010kg$
Mass of each marble,$m=5g=0.005kg$
Suppose the number of marbles striking the disc per second=n and velocity with which marbles strike disc is v.
Then Weight of disc acting downward$=Mg$
Change in velocity of marbles when they rebound $=v-(-v)=2v$
Therefore the change in momentum of each marble when it strikes the disc=$m * 2v=2mv$
and total momentum imparted per second to the disc$=2mnv $= The force exerted by the marbles in the upward direction
The disc will remain at rest if the net force acting on it is zero provided it is initially at rest.
Therefore for the disc to remain at rest,
Weight of disc=Upward force on it
$= Mg=2mnv$
$v=\dfrac{Mg}{2mn}=\dfrac{(0.010 *9.8)}{(2*0.005*10)}$
$=0.98 m/s$

Choose the wrong statement

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. $1 kg \ wt = 9.8 N$

  2. Momentum is a vector quantity

  3. Force is always conserved

  4. Momentum is conserved in the absence of an external force

Show answer
Correct Option: C
Explanation:

Forces that do not store energy are called nonconservative or dissipative forces. Friction is a nonconservative force, and there are others. Any friction-type force, like air resistance, is a nonconservative force.

Force is always conserved is the wrong statement.

A long-jumper runs before jumping because

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. He covers a greater distance

  2. He maintains momentum conservation

  3. He gains energy by running

  4. He gains momentum

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Correct Option: D
Explanation:

to gain momentum so that the range that he jumps is long

A body of mass $5  kg$ undergoes a change in speed form $30 m/s$ to $40  {m}/{s}$. Its momentum would increase by

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. $50 kg {m}/{s}$

  2. $75 kg {m}/{s}$

  3. $150 kg {m}/{s}$

  4. $350 kg {m}/{s}$

Show answer
Correct Option: A
Explanation:

change in momentum = 5 (40 - 30) = $50kgm/s$

A number of discs, each of momentum $M  kg  {m}/{s}$ are striking a wall at the rate of $n$ discs per minute. The force associated with these discs, in newtons, would be

physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. $\displaystyle\frac{Mn}{60}$

  2. $60 Mn$

  3. $\displaystyle\frac{M}{60n}$

  4. $\displaystyle\frac{n}{60M}$

Show answer
Correct Option: A
Explanation:

The force is $F=\dfrac{\Delta P}{dt}$

$momentum=M kg.m/s$
change in time=rate of dics striking wall 
$\Delta t=\dfrac{1}{n/minute}=\dfrac{60}{n}$ 
$F=\dfrac{\Delta P}{dt}=\dfrac{M}{60/n}=\dfrac{Mn}{60}N$