Tag: physics

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

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $=M _{B}V _{B}=Ft$

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

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

  1. reduced to half

  2. doubled

  3. quadrupled

  4. kept unchanged
Reveal answer Fill a bubble to check yourself
A Correct answer
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 ${P}'=\frac{P}{2}$
      $\frac{P}{2}=M{V}'$
       ${V}'=\frac{V}{2}$

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

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

  1. $600N$

  2. $1200N$

  3. $1350N$

  4. $1950N$
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

Momentum is a measure of:

  1. weight

  2. mass

  3. quantity of motion

  4. velocity
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

Momentum has the same units as that of:

  1. impulse

  2. torque

  3. moment of momentum

  4. couple
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $Kgms^{-1}$

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

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

  1. $250N$

  2. $125N$

  3. $0N$

  4. $3.78N$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $V _f=10m/s,V _i=0m/s$

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

$F=0.25(500)$

$F=25\times 5$

$\boxed{F=125N}$

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

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

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