# A bob of mass m attached to an inextensible string of length l is suspended from vertical support.  The bob rotates in a horizontal circle with an angular speed $\mathrm{\omega }$ $\mathrm{rad}/\mathrm{s}$ about the vertical.  About the point of suspension. 1.  Angular momentum is conserved 2. Angular momentum changes in magnitude but not in the direction 3. Angular momentum changes in direction but not in magnitude 4. Angular momentum changes both in direction and magnitude

Subtopic:  Angular Momentum |
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In free space, a rifle of mass M shoots a bullet of mass m at a stationary block of mass M at a distance D away from it. When the bullet has moved through a distance d towards the block, the centre of mass of the bullet - block system is at a distance of

1. $\frac{\left(D-d\right)}{M+m}$ from the bullet

2. $\frac{md+MD}{M+m}$ from the block

3. $\frac{2md+MD}{M+m}$ from the block

4. $\frac{\left(D-d\right)M}{M+m}$ from the bullet

Subtopic:  Center of Mass |
57%
From NCERT
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Blocks A and B are resting on a smooth horizontal surface given equal speeds of 2 m/s in the opposite sense as shown in the figure.

At t = 0, the position of blocks are shown, then the coordinates of centre of mass at t = 3s will be

1.  (1, 0)

2.  (3, 0)

3.  (5, 0)

4.  (2.25, 0)

Subtopic:  Center of Mass |
74%
From NCERT
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A wheel is at rest. Its angular velocity increases uniformly and becomes 80 rad/s after 5 s. The total angular displacement is

Subtopic:  Rotational Motion: Kinematics |
70%
From NCERT
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A force$$- F \hat k$$ acts on O, the origin of the coordinate system. The torque at the point (1, -1) will be:

1. $-\mathrm{F}\left(\stackrel{^}{\mathrm{i}}+\stackrel{^}{\mathrm{j}}\right)$

2. $\mathrm{F}\left(\stackrel{^}{\mathrm{i}}+\stackrel{^}{\mathrm{j}}\right)$

3. $-\mathrm{F}\left(\stackrel{^}{\mathrm{i}}-\stackrel{^}{\mathrm{j}}\right)$

4. $\mathrm{F}\left(\stackrel{^}{\mathrm{i}}-\stackrel{^}{\mathrm{j}}\right)$

Subtopic:  Torque |
From NCERT
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Moment of inertia of an object does not depend upon

1.  mass of object

2.  mass distribution

3.  angular velocity

4.  axis of rotation

Subtopic:  Moment of Inertia |
78%
From NCERT
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A thin uniform circular disc of mass M and radius R is rotating in a horizontal plane about an axis passing through its center and perpendicular to its plane with an angular velocity $\omega$. Another disc of the same dimensions but of mass $\frac{1}{4}M$ is placed gently on the first disc co-axially. The angular velocity of the system will be:

 1 $\frac{2}{3}\mathrm{\omega }$ 2 $\frac{4}{5}\mathrm{\omega }$ 3 $\frac{3}{4}\mathrm{\omega }$ 4 $\frac{1}{3}\mathrm{\omega }$
Subtopic:  Angular Momentum |
81%
From NCERT
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When a torque acting upon a system is zero, then which of the following will be constant

1.  force

2.  Linear momentum

3.  Angular momentum

4.  Linear impulse

Subtopic:  Angular Momentum |
86%
From NCERT
PMT - 1997
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Consider a system of two particles having masses . If the particle of mass ${\mathrm{m}}_{1}$ is pushed towards the center of mass of particles through a distance, by what distance would be the particle of the mass ${\mathrm{m}}_{2}$ move so as to keep the center of mass of particles at the original position?

1.

2.  $\frac{{\mathrm{m}}_{1}}{{\mathrm{m}}_{2}}\mathrm{d}$

3.  d

4.  $\frac{{\mathrm{m}}_{2}}{{\mathrm{m}}_{1}}\mathrm{d}$

Subtopic:  Center of Mass |
55%
From NCERT
PMT - 2004
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A flywheel is in the form of a uniform circular disc of radius 1 m and mass 2 kg. The work which must be done on it to increase its frequency of rotation from 5 rev ${\mathrm{s}}^{-1}$ to 10 rev ${\mathrm{s}}^{-1}$ is approximately

1.  1.5 x ${10}^{2}$ J

2.  3.0 x ${10}^{2}$ J

3.  1.5 x ${10}^{3}$ J

4.  3.0 x ${10}^{3}$ J

Subtopic:  Rotational Motion: Kinematics |
58%
From NCERT
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