Tag: law of conservation of angular momentum

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Questions Related to law of conservation of angular momentum

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 of mass m travels with a speed v along positive direction of x-axis parallel to the line y=4. At t=0, the particle is at (0,4),. The angular momentum of the particle about the origin is 

  1. 0

  2. 4 mv directed along the positive z- axis

  3. 4 mv directed along the negative z- axis

  4. 4 mv directed along the positive y- axis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The correct option is C

We have,

$Mass=m,Speed=v$

A particle is moving along a straight line parallel to the y-axis.

So, position vector $(\hat r ) = 4 \hat j$ 

velocity of body $\hat V = v \hat i$

Since we know,

Angular momentum = $m(\hat r \times\hat V)$

$=m ( 4 \hat j \times v \hat i)$

$=-4mv\hat k$

Since,

$I \times j = k$ 
And, $j \times i = - k$
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 spinning ice skater can increase his rate of rotation by bringing is arms and free leg closer to his body.
How does this procedure affect the skater's angular momentum and kinetic energy?

  1. Angular momentum remains the same while kinetic energy increases

  2. Angular momentum remains the same while kinetic energy decreases

  3. Both angular momentum and kinetic energy remain the same

  4. Angular momentum increases while kinetic energy remains the same
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 angular momentum of a moving body remains constant if

  1. net external force is applied

  2. net pressure is applied

  3. net external torque is applied

  4. net external torque is not appled
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Angular momentum is conserved when the net external torque on a system is zero. Torque, not force or pressure, is what changes angular momentum. The absence of net external torque means angular momentum remains constant.

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

Which of the following laws is not always true as per the present world?

  1. Law of conservation of Angular momentum

  2. Law of conservation of Charge 

  3. Law of conservation of linear momentum

  4. Law of conservation of Energy 
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The law of conservation of linear momentum is generally true for isolated systems, but in the presence of external forces (which are ubiquitous), it is not always conserved for a specific body. However, in the context of fundamental physics, all listed conservation laws are highly robust, but linear momentum is often cited as the one most easily 'broken' by external forces.

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 should be the angular momentum of an electron in Bohr's hydrogen atom whose energy is -0.544 eV?

  1. $\large \frac{h}{\pi}$

  2. $\large \frac{3h}{2\pi}$

  3. $\large \frac{5h}{2\pi}$

  4. $\dfrac{2h}{2\pi}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Energy E = -13.6 / n^2 eV. Given E = -0.544 eV, n^2 = 13.6 / 0.544 = 25, so n = 5. Bohr's quantization condition is L = n * h / (2 * pi). For n = 5, L = 5h / (2 * pi).

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

Which parameters of all the particles of rotating fan are same :-

  1. Only angular $( \theta, \omega, \alpha)$

  2. Only linear (s,v,a)

  3. Both linear and angular

  4. None of them
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a rotational motion, only the angular parameters ($\theta, w,\alpha$) are same but not the linear parameters.

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, sitting firmly over a rotating stool has his arms stretched. If he folds his arms, the work done by the man is :

  1. zero

  2. positive

  3. negative

  4. may be positive or negative
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the arms are stretched the rotational inertia is higher. When the man folds his arm he is basically decreasing his rotational inertia thereby gaining more angular velocity using the principle of conservation of angular momentum. This implies more angular distance is covered in the same time giving us positive work.