Tag: physics

Questions Related to physics

State whether true or false.
The linear momentum of a body at rest is zero.

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Linear momentum is given by 

$P=MV$   

M is Mass
V is Velocity

If $V=0$
   $P=0$

State whether true or false.
If the same force is applied on two bodies of different masses for the same time, then the change produced in the momentum of the two bodies is also the same.
physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Let A and B be two bodies and F be the force for t time duration.

    $a _{A}=\frac{F}{M _{A}}$  ,$a _{B}=\frac{F}{M _{B}}$
$V _{A}$ (after t)$=\frac{F _{t}}{M _{A}}$
$V _{B}$ (after t)$=\frac{F _{t}}{M _{B}}$
Momentum of A $=M _{A}V _{A}=Ft$
Momentum of B $=M _{B}V _{B}=Ft$

To reduce the momentum of a given body to half its original value, its velocity must be ___________.

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

  1. reduced to half

  2. doubled

  3. quadrupled

  4. kept unchanged

Show answer
Correct Option: A
Explanation:

The momentum of a body is given by

          $=MV$
where M is mass and V is velocity
           $P=MV$
So if M is constant and ${P}'=\frac{P}{2}$
      $\frac{P}{2}=M{V}'$
       ${V}'=\frac{V}{2}$

The momentum of a massive object at rest is

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

  1. Very large

  2. Very small

  3. Zero

  4. Infinity

Show answer
Correct Option: C
Explanation:

Momentum is defined as the product of the body's mass and its velocity.

$p = m \times v$
Here, object is at rest. Hence, velocity, $v = 0$.
Therefore, momentum is zero.

A parachutist with total weight $75kg$ drops vertically onto a sandy ground with a speed of $2m{ s }^{ -1 }$ and comes to a halt over a distance of $0.25m$. The average force from the ground on her is close to

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

  1. $600N$

  2. $1200N$

  3. $1350N$

  4. $1950N$

Show answer
Correct Option: A
Explanation:

Initial velocity while dropping on the ground u=2m/s.
Parachutist was brought to rest within s=0.25 m
Therefore retardation f : $u^2=2fs; \; f=\frac{u^2}{2s}=8m/s^2$
Averarage force from ground on her close is F=mf=600 N

Which of the following statements is/are correct for internal forces?

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

  1. They are always balanced

  2. They are never balanced

  3. They may or may not be balanced

  4. none of these

Show answer
Correct Option: C
Explanation:

An internal force acting on a system may be balanced or unbalanced.

Momentum is a measure of:

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

  1. weight

  2. mass

  3. quantity of motion

  4. velocity

Show answer
Correct Option: C
Explanation:

In order to stop a moving body we require a force and depends on the velocity as well as its mass. It was Newton in his second law who defined this new quantity as momentum.
Momentum is the product of mass and velocity of the body or in other words momentum is the measure of quantity of motion.

Momentum has the same units as that of:

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

  1. impulse

  2. torque

  3. moment of momentum

  4. couple

Show answer
Correct Option: A
Explanation:

Momentum = mass $\times$ velocity and its unit is $Kgms^{-1}$
Impulse of the force(J) =force $\times$ time and 
$=ma \times t$
$=m\left(\dfrac{u}{t}\right) \times t$
Thus, impulse (J) is the change of momentum and its unit is $Kgms^{-1}$

A football player kicks a $0.25kg$ ball and imparts it a velocity of $10m/s$. The contact between foot and the ball is only $\cfrac{1}{50}$th of a second. The kicking force is

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

  1. $250N$

  2. $125N$

  3. $0N$

  4. $3.78N$

Show answer
Correct Option: B
Explanation:

Force = $\dfrac{\triangle P}{\triangle t}$ (Newtons 2nd law)


$F=\dfrac{m\triangle V}{\triangle f}=\dfrac{m(V _f-V _i)}{\triangle f}$

Force, $m=0.25kg$

and $V _f=10m/s,V _i=0m/s$

$\therefore F=\dfrac{(0.25)(10-0)}{\dfrac{1}{50}}$

$F=0.25(500)$

$F=25\times 5$

$\boxed{F=125N}$

A bullet of mass $40\ g$ is fired from a gun of mass $10\ kg$. If velocity of bullet is $400\ m/s$, then the recoil velocity of the gun will be

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

  1. $1.6\ m/s$ in the direction of the bullet

  2. $1.6\ m/s$ opposite to the direction of the bullet

  3. $1.8\ m/s$ in the direction of the bullet

  4. $1.8\ m/s$ opposite to the direction of the bullet

Show answer
Correct Option: B
Explanation:

Let velocity of gun is $v$. 

There is no external force acting, so linear momentum will conserve.
Before the firing, Linear Momentum $=0$
After the firing, Linear momentum $= 0.04 \times 400 + 10\times v$
$\Rightarrow  0.04\times 400 + 10 \times v=0$         $\Rightarrow v= -1.6 m/s$
Hence, $1.6 m/s $ opposite to the direction of the bullet.