Rotational Motion
Q. If a rotating body has an angular momentum of L and its moment of inertia is I, what is the angular velocity ω of the body?
A.
L/I
B.
I/L
C.
L^2/I
D.
I^2/L
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Solution
Angular momentum L = Iω, thus ω = L/I.
Correct Answer: A — L/I
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Q. If a rotating object has a moment of inertia of 4 kg·m² and is spinning with an angular velocity of 3 rad/s, what is its angular momentum?
A.
12 kg·m²/s
B.
4 kg·m²/s
C.
1 kg·m²/s
D.
7 kg·m²/s
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Solution
Angular momentum L = Iω = 4 kg·m² * 3 rad/s = 12 kg·m²/s.
Correct Answer: A — 12 kg·m²/s
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Q. If a rotating object has a moment of inertia of 5 kg·m² and is rotating with an angular velocity of 3 rad/s, what is its angular momentum?
A.
15 kg·m²/s
B.
5 kg·m²/s
C.
8 kg·m²/s
D.
10 kg·m²/s
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Solution
Angular momentum L is given by L = Iω. Thus, L = 5 kg·m² * 3 rad/s = 15 kg·m²/s.
Correct Answer: A — 15 kg·m²/s
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Q. If a rotating object has a moment of inertia of 5 kg·m² and is spinning with an angular velocity of 3 rad/s, what is its angular momentum?
A.
15 kg·m²/s
B.
5 kg·m²/s
C.
8 kg·m²/s
D.
10 kg·m²/s
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Solution
Angular momentum L = Iω = 5 kg·m² * 3 rad/s = 15 kg·m²/s.
Correct Answer: A — 15 kg·m²/s
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Q. If a rotating object has a moment of inertia of I and is rotating with an angular velocity ω, what is its rotational kinetic energy?
A.
1/2 Iω
B.
1/2 Iω^2
C.
Iω^2
D.
Iω
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Solution
The rotational kinetic energy is given by KE = 1/2 Iω^2.
Correct Answer: B — 1/2 Iω^2
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Q. If a solid cylinder is rotated about its diameter, what is its moment of inertia?
A.
1/2 MR^2
B.
1/4 MR^2
C.
1/3 MR^2
D.
MR^2
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Solution
The moment of inertia of a solid cylinder about its diameter is I = 1/4 MR^2.
Correct Answer: B — 1/4 MR^2
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Q. If a solid cylinder rolls without slipping, what fraction of its total kinetic energy is translational?
A.
1/3
B.
1/2
C.
2/3
D.
1
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Solution
For a solid cylinder, the total kinetic energy is KE_total = KE_translational + KE_rotational = (1/2)mv^2 + (1/2)(1/2)mR^2(ω^2). Since ω = v/R, the translational part is 2/3 of the total.
Correct Answer: C — 2/3
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Q. If a solid disk rolls without slipping, what fraction of its total energy is translational at the bottom of an incline?
A.
1/4
B.
1/3
C.
1/2
D.
2/3
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Solution
For a solid disk, the translational kinetic energy is 1/3 of the total kinetic energy when rolling without slipping.
Correct Answer: B — 1/3
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Q. If a solid sphere and a hollow sphere have the same mass and radius, which one will roll down an incline faster?
A.
Solid sphere
B.
Hollow sphere
C.
Both will roll at the same speed
D.
Depends on the angle of incline
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Solution
The solid sphere will roll down the incline faster because it has a smaller moment of inertia compared to the hollow sphere.
Correct Answer: A — Solid sphere
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Q. If a solid sphere and a solid cylinder of the same mass and radius are released from rest at the same height, which will have a greater speed at the bottom?
A.
Solid sphere
B.
Solid cylinder
C.
Both have the same speed
D.
Depends on the mass
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Solution
Both will have the same speed at the bottom due to conservation of energy, as they start from the same height.
Correct Answer: C — Both have the same speed
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Q. If a solid sphere of mass M and radius R is rotating about an axis through its center, what is its moment of inertia?
A.
2/5 MR^2
B.
3/5 MR^2
C.
1/2 MR^2
D.
1/3 MR^2
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Solution
The moment of inertia of a solid sphere about an axis through its center is I = 2/5 MR^2.
Correct Answer: A — 2/5 MR^2
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Q. If a solid sphere of radius R and mass M is rotating about an axis through its center, what is its moment of inertia?
A.
2/5 MR^2
B.
3/5 MR^2
C.
1/2 MR^2
D.
1/3 MR^2
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Solution
The moment of inertia of a solid sphere about its center is I = 2/5 MR^2.
Correct Answer: A — 2/5 MR^2
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Q. If a torque of 15 Nm is produced by a force acting at a distance of 0.3 m from the pivot, what is the magnitude of the force?
A.
50 N
B.
45 N
C.
40 N
D.
30 N
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Solution
Force = Torque / Distance = 15 Nm / 0.3 m = 50 N.
Correct Answer: A — 50 N
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Q. If a torque of 25 Nm is applied and the lever arm is 5 m, what is the angle at which the force is applied if the force is 10 N?
A.
0 degrees
B.
30 degrees
C.
60 degrees
D.
90 degrees
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Solution
Torque = Force × Distance × sin(θ) => 25 Nm = 10 N × 5 m × sin(θ) => sin(θ) = 0.5 => θ = 30 degrees.
Correct Answer: C — 60 degrees
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Q. If a torque of 25 Nm is applied to a wheel with a radius of 0.5 m, what is the force applied at the edge of the wheel?
A.
50 N
B.
40 N
C.
30 N
D.
20 N
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Solution
Force = Torque / Radius = 25 Nm / 0.5 m = 50 N.
Correct Answer: A — 50 N
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Q. If a torque of 25 Nm is generated by a force acting at a distance of 0.5 m, what is the force applied?
A.
50 N
B.
40 N
C.
30 N
D.
20 N
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Solution
Force = Torque / Distance = 25 Nm / 0.5 m = 50 N.
Correct Answer: A — 50 N
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Q. If a torque of 30 Nm is applied to a lever arm of 3 m, what is the force applied?
A.
5 N
B.
10 N
C.
15 N
D.
20 N
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Solution
Force = Torque / Distance = 30 Nm / 3 m = 10 N.
Correct Answer: B — 10 N
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Q. If a torque of 5 Nm is applied to a rotating object with a moment of inertia of 2 kg·m², what is the angular acceleration?
A.
2.5 rad/s²
B.
5 rad/s²
C.
10 rad/s²
D.
1 rad/s²
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Solution
Angular acceleration α = Torque / Moment of inertia = 5 Nm / 2 kg·m² = 2.5 rad/s².
Correct Answer: A — 2.5 rad/s²
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Q. If a torque of 8 Nm is produced by a force acting at a distance of 0.2 m, what is the force?
A.
20 N
B.
30 N
C.
40 N
D.
50 N
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Solution
Force = Torque / Distance = 8 Nm / 0.2 m = 40 N.
Correct Answer: A — 20 N
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Q. If a wheel of radius R rolls without slipping, what is the distance traveled by the center of mass after one complete rotation?
A.
2πR
B.
πR
C.
4R
D.
R/2
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Solution
The distance traveled by the center of mass after one complete rotation is equal to the circumference of the wheel, which is 2πR.
Correct Answer: A — 2πR
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Q. If the angle between the force and the lever arm is 90 degrees, how does it affect the torque?
A.
Torque is zero
B.
Torque is maximum
C.
Torque is half
D.
Torque is minimum
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Solution
Torque is maximum when the angle is 90 degrees because τ = F × r × sin(θ) and sin(90°) = 1.
Correct Answer: B — Torque is maximum
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Q. If the angle between the force and the lever arm is 90 degrees, what is the torque produced by a 15 N force applied at a distance of 2 m?
A.
0 Nm
B.
15 Nm
C.
30 Nm
D.
45 Nm
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Solution
Torque (τ) = F × d × sin(θ) = 15 N × 2 m × sin(90°) = 30 Nm.
Correct Answer: C — 30 Nm
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Q. If the angular momentum of a rotating object is conserved, what can be said about its moment of inertia and angular velocity?
A.
Both increase
B.
Both decrease
C.
One increases and the other decreases
D.
Remain constant
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Solution
If angular momentum is conserved, an increase in moment of inertia results in a decrease in angular velocity, and vice versa.
Correct Answer: C — One increases and the other decreases
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Q. If the angular momentum of a rotating object is doubled while its moment of inertia remains constant, what happens to its angular velocity?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Increases by a factor of 4
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Solution
Angular momentum L = Iω; if L is doubled and I remains constant, ω must also double.
Correct Answer: A — Doubles
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Q. If the angular momentum of a system is conserved, which of the following statements is true?
A.
Net external torque is zero
B.
Net external force is zero
C.
Kinetic energy is conserved
D.
Linear momentum is conserved
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Solution
Angular momentum is conserved when the net external torque acting on the system is zero.
Correct Answer: A — Net external torque is zero
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Q. If the angular momentum of a system is zero, what can be said about the motion of the system?
A.
It is at rest
B.
It is moving linearly
C.
It is rotating
D.
It can be in any motion
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Solution
Zero angular momentum does not imply rest; it can be in linear motion.
Correct Answer: D — It can be in any motion
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Q. If the angular momentum of a system is zero, what can be said about the motion of the particles in the system?
A.
They are at rest
B.
They are moving in a straight line
C.
They are rotating
D.
They are in circular motion
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Solution
Zero angular momentum implies no net rotation; particles can still move linearly.
Correct Answer: B — They are moving in a straight line
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Q. If the lever arm is doubled while keeping the force constant, how does the torque change?
A.
It doubles
B.
It triples
C.
It remains the same
D.
It halves
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Solution
Torque is directly proportional to the lever arm; if the lever arm is doubled, the torque also doubles.
Correct Answer: A — It doubles
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Q. If the moment of inertia of a body is 10 kg m², what is the angular momentum when it rotates with an angular velocity of 5 rad/s?
A.
50 kg m²/s
B.
10 kg m²/s
C.
5 kg m²/s
D.
2 kg m²/s
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Solution
Angular momentum L = Iω = 10 kg m² * 5 rad/s = 50 kg m²/s.
Correct Answer: A — 50 kg m²/s
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Q. If the moment of inertia of a body is 10 kg m², what is the rotational kinetic energy when it rotates with an angular velocity of 5 rad/s?
A.
125 J
B.
50 J
C.
100 J
D.
75 J
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Solution
Rotational kinetic energy is given by KE = 1/2 I ω² = 1/2 * 10 * 5² = 125 J.
Correct Answer: A — 125 J
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