Rotational Motion
Q. If the moment of inertia of a body is 10 kg·m² and it is subjected to a torque of 20 N·m, what is the angular acceleration?
A.
2 rad/s²
B.
0.5 rad/s²
C.
5 rad/s²
D.
10 rad/s²
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Solution
Using τ = Iα, we have α = τ/I = 20 N·m / 10 kg·m² = 2 rad/s².
Correct Answer: A — 2 rad/s²
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Q. If the moment of inertia of a body is doubled, what happens to its rotational kinetic energy if the angular velocity remains constant?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Quadruples
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Solution
Rotational kinetic energy is given by KE = 1/2 I ω^2. If I is doubled and ω remains constant, KE also doubles.
Correct Answer: A — Doubles
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Q. If the moment of inertia of a body is doubled, what will be the effect on its angular acceleration if the torque applied remains constant?
A.
Doubles
B.
Halves
C.
Remains the same
D.
Increases by a factor of four
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Solution
Angular acceleration α = τ/I. If I is doubled and τ remains constant, α is halved.
Correct Answer: B — Halves
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Q. If the moment of inertia of a body is increased, what happens to its angular acceleration for a constant torque?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
According to Newton's second law for rotation, τ = Iα, if I increases and τ is constant, α must decrease.
Correct Answer: B — Decreases
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Q. If the radius of a disc is doubled while keeping its mass constant, how does its moment of inertia change?
A.
It remains the same
B.
It doubles
C.
It quadruples
D.
It halves
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Solution
The moment of inertia of a disc is I = 1/2 MR^2. If R is doubled, I becomes 1/2 M(2R)^2 = 2MR^2, which is quadrupled.
Correct Answer: C — It quadruples
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Q. If the radius of a disk is doubled while keeping its mass constant, how does its moment of inertia change?
A.
Increases by a factor of 2
B.
Increases by a factor of 4
C.
Remains the same
D.
Decreases by a factor of 4
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Solution
The moment of inertia of a disk is I = 1/2 MR^2. If R is doubled, I becomes 1/2 M(2R)^2 = 2MR^2, which is 4 times the original.
Correct Answer: B — Increases by a factor of 4
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Q. If the radius of a rotating disc is doubled while keeping the mass constant, how does the angular momentum change if the angular velocity remains the same?
A.
It doubles
B.
It remains the same
C.
It quadruples
D.
It halves
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Solution
Angular momentum L = Iω; if radius is doubled, moment of inertia I increases by a factor of 4, hence L quadruples.
Correct Answer: C — It quadruples
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Q. If the radius of a rotating object is halved while keeping the angular velocity constant, what happens to the linear velocity at the edge?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It becomes zero
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Solution
Linear velocity v = rω. If r is halved and ω remains constant, v also halves.
Correct Answer: B — It halves
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Q. If the radius of a rotating object is halved while keeping the mass constant, how does its moment of inertia change?
A.
It remains the same
B.
It doubles
C.
It halves
D.
It reduces to one-fourth
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Solution
Moment of inertia I is proportional to the square of the radius, so halving the radius reduces I to one-fourth.
Correct Answer: D — It reduces to one-fourth
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Q. If the radius of a rotating wheel is halved while keeping the angular velocity constant, what happens to the linear velocity of a point on the edge of the wheel?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It becomes zero
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Solution
Linear velocity v = rω; if r is halved and ω remains constant, v is halved.
Correct Answer: B — It halves
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Q. If the radius of a solid disk is doubled while keeping its mass constant, how does its moment of inertia change?
A.
Increases by a factor of 2
B.
Increases by a factor of 4
C.
Remains the same
D.
Decreases by a factor of 2
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Solution
The moment of inertia of a solid disk is I = 1/2 MR^2. If R is doubled, I becomes 1/2 M(2R)^2 = 2MR^2, which is 4 times the original.
Correct Answer: B — Increases by a factor of 4
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Q. If the torque is doubled while keeping the distance constant, what happens to the force applied?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
Torque = Force × Distance; if Torque is doubled and Distance is constant, Force must also double.
Correct Answer: A — It doubles
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Q. If the torque on an object is zero, what can be said about the forces acting on it?
A.
The object is at rest.
B.
The net force is zero.
C.
The forces are balanced.
D.
The forces are acting along the same line.
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Solution
If the torque is zero, it means that the forces are acting along the same line, resulting in no rotational effect.
Correct Answer: D — The forces are acting along the same line.
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Q. If the torque on an object is zero, which of the following must be true?
A.
The net force is zero.
B.
The object is at rest.
C.
The forces are balanced.
D.
The line of action of the forces passes through the pivot.
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Solution
If the torque is zero, it means that the line of action of the forces passes through the pivot point.
Correct Answer: D — The line of action of the forces passes through the pivot.
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Q. If two equal and opposite forces are applied at the ends of a lever arm of length 4 m, what is the net torque about the center?
A.
0 Nm
B.
8 Nm
C.
4 Nm
D.
16 Nm
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Solution
The net torque is zero because the forces are equal and opposite, resulting in no rotational effect.
Correct Answer: A — 0 Nm
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Q. If two equal and opposite forces are applied at the ends of a lever arm of length 1 m, what is the net torque about the center?
A.
0 Nm
B.
1 Nm
C.
2 Nm
D.
4 Nm
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Solution
The net torque is zero because the forces are equal and opposite, producing no rotational effect.
Correct Answer: A — 0 Nm
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Q. If two equal and opposite forces are applied at the ends of a lever arm, what is the net torque about the center?
A.
Zero
B.
Equal to the force
C.
Depends on the distance
D.
Twice the force
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Solution
The net torque is zero because the forces are equal and opposite, producing no rotational effect.
Correct Answer: A — Zero
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Q. If two forces of 5 N and 10 N are applied at the same distance from a pivot, which force produces more torque?
A.
5 N
B.
10 N
C.
Both produce the same torque
D.
It depends on the angle of application
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Solution
Torque is directly proportional to the force applied; hence, the 10 N force produces more torque.
Correct Answer: B — 10 N
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Q. If two forces of equal magnitude are applied at different distances from a pivot, which will produce a greater torque?
A.
The force applied further away
B.
The force applied closer
C.
Both produce equal torque
D.
It depends on the angle
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Solution
Torque is greater when the force is applied further away from the pivot, given equal magnitudes.
Correct Answer: A — The force applied further away
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Q. If two forces of equal magnitude are applied at opposite ends of a lever arm, what is the net torque about the center?
A.
Zero
B.
Equal to the force
C.
Twice the force
D.
Depends on the distance
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Solution
The net torque is zero because the torques produced by the two forces cancel each other out.
Correct Answer: A — Zero
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Q. If two identical disks are stacked on top of each other, what is the moment of inertia about the axis of the bottom disk?
A.
MR^2
B.
2MR^2
C.
1/2 MR^2
D.
4MR^2
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Solution
The moment of inertia of the bottom disk is MR^2, and the top disk contributes an additional MR^2 due to the parallel axis theorem, giving a total of 2MR^2.
Correct Answer: B — 2MR^2
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Q. If two rigid bodies have the same mass and shape but one is rotating faster than the other, how does their moment of inertia compare?
A.
The same
B.
The faster one has a larger moment of inertia
C.
The slower one has a larger moment of inertia
D.
Cannot be determined
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Solution
The moment of inertia depends only on the mass distribution and shape, not on the angular velocity.
Correct Answer: A — The same
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Q. In a rotating system, if the angular momentum is doubled while the moment of inertia remains constant, what happens to the angular velocity?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
Since L = Iω, if L is doubled and I remains constant, then ω must also double.
Correct Answer: A — It doubles
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Q. In a seesaw, if one child exerts a force of 30 N at a distance of 2 m from the pivot, what is the torque exerted by that child?
A.
15 Nm
B.
30 Nm
C.
60 Nm
D.
0 Nm
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Solution
Torque (τ) = F × r = 30 N × 2 m = 60 Nm.
Correct Answer: C — 60 Nm
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Q. In a seesaw, if one child exerts a torque of 30 N·m on one side, what torque must the other child exert to balance it?
A.
15 N·m
B.
30 N·m
C.
45 N·m
D.
60 N·m
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Solution
To balance the seesaw, the other child must exert an equal torque of 30 N·m.
Correct Answer: B — 30 N·m
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Q. In a system of two particles, if one particle has an angular momentum of L1 and the other has L2, what is the total angular momentum of the system?
A.
L1 + L2
B.
L1 - L2
C.
L1 * L2
D.
L1 / L2
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Solution
Total angular momentum of the system is the vector sum of individual angular momenta: L_total = L1 + L2.
Correct Answer: A — L1 + L2
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Q. In a system of two rotating bodies, if one body has twice the moment of inertia of the other, how does their angular momentum compare if they rotate with the same angular velocity?
A.
The same
B.
Twice as much
C.
Half as much
D.
Four times as much
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Solution
Angular momentum L = Iω; if one has twice the moment of inertia, it will have twice the angular momentum at the same angular velocity.
Correct Answer: B — Twice as much
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Q. In a system of two rotating disks, if disk A has twice the moment of inertia of disk B and they are both rotating with the same angular velocity, what can be said about their angular momentum?
A.
LA = LB
B.
LA = 2LB
C.
LA = 4LB
D.
LA = 1/2 LB
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Solution
Angular momentum L = Iω; since IA = 2IB and ωA = ωB, LA = 2LB.
Correct Answer: B — LA = 2LB
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Q. In rolling motion, which type of energy is associated with the rotation of the object?
A.
Translational kinetic energy
B.
Rotational kinetic energy
C.
Potential energy
D.
Elastic potential energy
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Solution
Rotational kinetic energy is associated with the rotation of the object in rolling motion.
Correct Answer: B — Rotational kinetic energy
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Q. The moment of inertia of a composite body can be calculated using which theorem?
A.
Pythagorean theorem
B.
Parallel axis theorem
C.
Perpendicular axis theorem
D.
Conservation of energy
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Solution
The moment of inertia of a composite body can be calculated using the parallel axis theorem.
Correct Answer: B — Parallel axis theorem
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