Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

Choose the INCORRECT statements

  1. If Linear momentum of system is conserved then angular momentum of system must be also conserved.

  2. If angular momentum is conserved then angular velocity must be also conserved about the same axis.

  3. If not torque about any axis is zero then force must also be zero.

  4. If a rigid body is in translational equilibrium then its linear velocity is constant but angular velocity may be varying
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

If a rigid body is in translational equilibrium, the net force is zero, but the angular velocity can be constant or changing depending on the net torque. The statement that angular velocity must be constant is incorrect.

Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

A satellite with a mass of $M$ moves in a circular orbit of radius $R$ at a constant speed of $v$. Which of the following must be true?
(I) The net force on the satellite is equal to MR and is directed toward the centre of the orbit,
(II) The net work done on the satellite by gravity in one revolution is zero.
(III) The angular momentum of the satellite is constant.

  1. I only

  2. III only

  3. I and II only

  4. II and III only

  5. I, II and III
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

The total angular momentum of a body is equal to the angular momentum  of its center of mass if the body has:

  1. only rotational motion

  2. only translational motion

  3. both rotational and translational motion

  4. no motion at all
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

 Two bodies of different masses have same K.E. The one having more momentum is

  1. Heavier body

  2. lighter body

  3. both none

  4. both
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$K.E.$ for a given momentum is inversely proportional to the mass$.$

So$,$ the lighter mass has greater kinetic energy$.$ For two bodies having same kinetic energy$,$ the heavier one has greater momentum$.$
Hence,
option $(B)$ is correct answer.  

Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

A force $\vec F = \alpha \hat i + 3\hat j + 6\hat k$ is acting at a point $\vec r = 2\hat i - 6\hat j - 12\hat k$. The value of $\alpha$ for which angular momentum about the origin is conserved is:-

  1. $1$

  2. $-1$

  3. $2$

  4. zero
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given,
$\vec r=2\hat i-6\hat j-12\hat k$
$\vec F=\alpha\hat i +3\hat j+6\hat k$
For the conservation of angular momentum about origin, the torgue acting on the particle will be zero.
$\tau=\vec r\times \vec F$
$\vec r\times \vec F=0$
$(\alpha \hat i+3\hat j+6\hat k)\times (2\hat i-6\hat j-12\hat k)=0\hat i+0\hat j+0\hat k$
$\hat i(-36+36)-\hat j (12+12\alpha)+\hat k(6+6\hat k)=0\hat i+0\hat j+\hat k$
By equating it's coefficient, we get
$12+12\alpha =0$,   $6+6\alpha =0$
$12=-12\alpha$
$\alpha =-1$
The correct option is B.

Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

A unit mass at position vector $\vec { r } = ( 3 \hat { i } + 4 \hat { j } )$ is moving with a velocity $\vec { v } = ( 5 \hat { i } - 6 \hat { j } )$ What is the angular momentum of the body about the origin

  1. 2 units along $z$ -axis

  2. 38 units along $x$ -axis

  3. 38 units along $y$ -axis

  4. 38 units along $Z$ -axis
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

A man standing on a platform holds weights in his outstretched arms. The system rotates freely about a central vertical axis. If he now draws the weights inwards close to his body, 

  1. the angular velocity of the system will increase.

  2. the angular momentum of the system will decrease.

  3. the kinetic energy of the system will increase.

  4. he will have to expend some energy to draw the weights in.
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

When the person contracts his hands he is decreasing his moment of inertia thereby increasing his angular velocity using the principle of conservation of angular momentum $I _1\omega _1=I _2\omega _2$
As the angular velocity increases, its kinetic energy also increases. Also energy would be required to draw the weights inwards from its position.

Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

A particle performs uniform circular motion with an angular momentum L. If the frequency of particle's motion is doubled and its kinetic energy halved, the angular momentum becomes:

  1. $2L$

  2. $4L$

  3. $ \mathrm{L} / 2 $

  4. $ \mathrm{L} / 4 $
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics rotational motion of a rigid body and moment of inertia angular momentum (l) and conservation of angular momentum angular momentum in case of rotation about a fixed axis law of conservation of angular momentum

What is the magnitude of vertical force required to produced a moment of 20 Nm at point A (1 m, 1 m) if the force is acting at point B (2m,2m)

  1. 40 N

  2. 30 N

  3. 20 N

  4. 10 N
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Moment = F * d_perpendicular. The force is vertical, so the perpendicular distance is the difference in x-coordinates: |2 - 1| = 1 m. 20 Nm = F * 1 m, so F = 20 N.