A flywheel has a mass of 25kg has a radius of 0.2m. What force should be applied tangentially to the rim of the flywheel so that it acquires an angular acceleration of 2rad/s2?
A.
2N
B.
5N
C.
3N
D.
1N
Answer: Option B
Explanation:
M = 25kg, R = 0.2m, α = 2rad/s2 Moment of inertia of the flywheel about its axis, I = 1/2 MR2=1/2×25×0.22=0.5kgm2 As torque, τ = F×R=I×α Therefore, Force F = Iα/R=(0.5×2)/0.2=5N.
The angular momentum of a body is 3.14 is and its rate of revolution is 10 cycles per second. Calculate the moment of inertia of the body about the axis of rotation?
A.
5 kgm2
B.
31.4 kgm2
C.
0
D.
0.5 kgm2
Answer: Option D
Explanation:
L = 3.14 Js v = 10 rps ω=2πv=2×3.14×10/rad As L = Iω I = L/ω = 3.14/(2×3.14×10)=0.5kgm2.
The angular velocity of a planet revolving in an elliptical orbit around the sun increases, when it comes closer to the sun. This is due to?
A.
Conservation of momentum
B.
Newton’s second law of motion
C.
Conservation of angular momentum
D.
Law of angular velocity
Answer: Option C
Explanation:
The angular velocity of a planet revolving in an elliptic orbit around the sun increases when it comes closer to the sun increases when it comes closer to the sun because its moment of inertia about the axis through the sun decreases. When it goes far away from the sun, its moment of inertia decreases so as to conserve angular momentum.
In a hand driven grinding machine, the handle is put?
A.
Perpendicular to the stone
B.
Near the circumference of the stone
C.
A few distances above the stone
D.
As far away from the stone
Answer: Option B
Explanation:
For a given force, torque can be increased if the perpendicular distance of the point of application of the force from the axis of rotation is increased. Hence the handle put near the circumference produces maximum torque.
