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SYSTEM OF PARTICLES AND ROTATIONAL MOTION

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Practice Test 11

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Angular momentum is

moment of momentum
product of mass and angular velocity
product of M.I. and velocity
moment of angular motion

Solution

Angular momentum= $\dot{r}$ ×(inearmomentum)

A gymnast takes turns with her arms & legs stretched. When she pulls her arms & legs in

the angular velocity decreases
the moment of inertia decreases
the angular velocity stays constant
the angular momentum increases

Solution

Since no external torque act on gymnast, so angular momentum (L=Iω) is conserved. After pulling her arms & legs, the angular velocity increases but moment of inertia of gymnast, decreases in, such a way that angular momentum remains constant.

If a running boy jumps on a rotating table, which of the following is conserved?

Linear momentum
K.E.
Angular momentum
None of these

Solution

The boy does not exert a torque to rotating table by jumping,so angular momentum is conserved i.e.,

$\frac{d\dot{L}}{dt}=0\Rightarrow \dot{L}= constant$

A simple pendulum is vibrating with angular amplitude of 90° as shown in figure.

For what value of θ is the acceleration directed

(i)vertically upwards

(ii)horizontally

(iii)vertically downwards

0°,cos^-1 ¹⁄_√3,90°
cos^-1 ¹⁄_√3,0°,90°
90°,cos^-1 ¹⁄_√3,0°
cos^-1 ¹⁄_√3,90°,0°

Solution

When θ = 0°, the net force is directed vertically upwards.

A projectile is thrown horizontally with a speed of 20 ms^-1. If g is 10 ms^-2, then the speed of the projectile after 5 second will be nearly

0.5 ms^-1
5 ms^-1
54 ms^-1
500 ms^-1

Solution

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SYSTEM OF PARTICLES AND ROTATIONAL MOTION

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