10 Question-Answer on rotational mechanics
1. A fly wheel rotating about a fixed axis has a kinetic energy of 360 joul when its angular speed is 30 radian/sec. The moment of inertia of the wheel about the axis of rotation is:
(a) 0.6 kg m2
(b) 0.15 kg m2
(c) 0.8 kg m2
(d) 0.75 kg m2
Ans: (c)
2. A rigid spherical body is spinning around an axis without any external torque. Due to change in temperature, the volume increases by 1%. Its angular speed will be:
(a) Increases approximately by 1%
(b) decreases approximately by 1%
(c) decreases approximately by0.67%
(d) decreases approximately by 0.33%
Ans: (c )
3. A thin uniform circular ring is rolling down an inclined plane of inclination 30˚ without slipping. Its linear acceleration along the inclined plane will be:
(a) g/2
(b) g/3
(c) g/4
(d) 2g/3
Ans:( c)
4. A spherical solid ball of 1 kg mass and radius 3 cm is rotating about an axis passing through its centre with an angular velocity of 50 rad/s. The kinetic energy of rotation is :
(a) 4500J
(b) 0.45 J
(c) 910 J
(d) 9/20 J
Ans: ( b)
5. A flywheel rotates with a uniform angular acceleration. Its angular velocity increases from 20 π rad/s to 40 π rad/s in 10 seconds. How many rotations did it make in this period?
(a) 80
(b) 100
(c) 120
(d) 150
Ans: (d)
6. Rotational motion can be
(a) One or two dimensional
(b) two or three dimensional
(c) three or one dimensional
(d) all of above
Ans: ( b)
7. Translation motion can be in :
(a) One dimension only
(b) Two dimension only
(c) Three dimensions only
(d) All of the above
Ans: (d)
8. Rotational analogue of force in linear motion is :
(a) Weight
(b) Angular momentum
(c) Moment of inertia
(d) Torque
Ans: ( d)
9. Dimensional formula of torque is same as that of:
(a) Power
(b) Angular momentum
(c) Angular impulse
(d) KE of rotation.
Ans : ( d)
`10. A person standing on a rotating platform with his hands lowered outstretches his arms. The angular momentum of the person:
(a) Increases
(b) Decreases
(c) Becomes zero
(d) Remains constant
Ans :( d)
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