Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

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 :

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

For metallic ball,

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

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

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 :

  1. $P$

  2. $2P$

  3. $zero$

  4. $-2P$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $=2P$

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

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) $

  1. $\displaystyle 0.98m/s$

  2. $\displaystyle 9.8m/s$

  3. $\displaystyle 1.96m/s$

  4. $\displaystyle 19.6m/s$
Reveal answer Fill a bubble to check yourself
A Correct answer
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
$= Mg=2mnv$
$v=\dfrac{Mg}{2mn}=\dfrac{(0.010 *9.8)}{(2*0.005*10)}$
$=0.98 m/s$
Multiple choice physics force and newton's laws of motion momentum (p) introduction to momentum linear momentum

Choose the wrong statement

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

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

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

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

  2. $60 Mn$

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

  4. $\displaystyle\frac{n}{60M}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

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