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Complete Syllabus Question Paper
Grade 11 : Physics - Rotational Motion (Set 4)— Questions & Detailed Solutions
Q1
Setup: A uniform thin rod of length $L = 2m$ and mass $M = 3kg$ is pivoted at one of its ends so that it can rotate freely in a plane.
Calculate the moment of inertia of the rod about an axis passing through the pivot perpendicular to its length.
(A)
$2\text{ kg m}^2$
(B)
$4\text{ kg m}^2$
(C)
$6\text{ kg m}^2$
(D)
$12\text{ kg m}^2$
Q2
Object Axis of Rotation Moment of Inertia ($I$) Object X Central axis perpendicular to disc plane $\frac{1}{2} M R^2$ Object Y Diameter axis $\frac{2}{5} M R^2$ Object Z Central axis perpendicular to ring plane $M R^2$
Based on the reference table, identify the geometry of objects X, Y, and Z respectively (all of mass $M$ and radius $R$).
| Object | Axis of Rotation | Moment of Inertia ($I$) |
|---|---|---|
| Object X | Central axis perpendicular to disc plane | $\frac{1}{2} M R^2$ |
| Object Y | Diameter axis | $\frac{2}{5} M R^2$ |
| Object Z | Central axis perpendicular to ring plane | $M R^2$ |
Based on the reference table, identify the geometry of objects X, Y, and Z respectively (all of mass $M$ and radius $R$).
(A)
Circular Disc, Solid Sphere, Thin Ring
(B)
Thin Ring, Solid Cylinder, Hollow Sphere
(C)
Solid Sphere, Circular Disc, Thin Ring
(D)
Circular Disc, Thin Ring, Solid Sphere
Q3
System Diagram: A circular ring of mass $M = 4kg$ and radius $R = 0.5m$ lies in the xy-plane. An axis is drawn tangent to the ring and parallel to its diameter in the plane.Determine the moment of inertia of the ring about this tangential axis in its plane.
System Diagram: A circular ring of mass $M = 4kg$ and radius $R = 0.5m$ lies in the xy-plane. An axis is drawn tangent to the ring and parallel to its diameter in the plane.
Determine the moment of inertia of the ring about this tangential axis in its plane.
(A)
$0.5\text{ kg m}^2$
(B)
$1.0\text{ kg m}^2$
(C)
$1.5\text{ kg m}^2$
(D)
$2.0\text{ kg m}^2$
Q4
A heavy flywheel starts from rest ($
\omega_0 = 0$) and undergoes constant angular acceleration of $\alpha = 4 rad/s^2for a duration oft = 5 s$.What is the total angular displacement covered by the flywheel during this time interval?
A heavy flywheel starts from rest ($
\omega_0 = 0$) and undergoes constant angular acceleration of $\alpha = 4 rad/s^2for a duration oft = 5 s$.
What is the total angular displacement covered by the flywheel during this time interval?
(A)
20 rad
(B)
40 rad
(C)
50 rad
(D)
100 rad
Q5
Vector Coordinates: Position vector of point of force application: $\vec{r} = (2\hat{i} + 1\hat{j})m$. Applied force vector: $\vec{F} = (3\hat{i} + 4\hat{j})\text{ N}$.Find the torque vector $\vec{\tau}$ acting about the origin.
Vector Coordinates: Position vector of point of force application: $\vec{r} = (2\hat{i} + 1\hat{j})m$. Applied force vector: $\vec{F} = (3\hat{i} + 4\hat{j})\text{ N}$.
Find the torque vector $\vec{\tau}$ acting about the origin.
(A)
$3\hat{k}\text{ N m}$
(B)
$5\hat{k}\text{ N m}$
(C)
$8\hat{k}\text{ N m}$
(D)
$11\hat{k}\text{ N m}$
Q6
A uniform solid spherical star contracts symmetrically under its own gravitational attraction to half its original radius ($R_2 = R_1 / 2$) without losing any mass ($M$ remains constant).Assuming no external torque acts on the star, what is the ratio of its new angular velocity $\omega_2$ to its initial angular velocity $\omega_1$?
A uniform solid spherical star contracts symmetrically under its own gravitational attraction to half its original radius ($R_2 = R_1 / 2$) without losing any mass ($M$ remains constant).
Assuming no external torque acts on the star, what is the ratio of its new angular velocity $\omega_2$ to its initial angular velocity $\omega_1$?
(A)
2
(B)
4
(C)
8
(D)
0.25
Q7
Track Geometry: Two particles A and B move along concentric circular paths of radius $R_A = 1m$ and $R_B = 2m$ respectively, fixed on a rotating rigid platform turning at angular speed $\omega = 3\text{ rad/s}$.What is the ratio of linear speed of particle B to that of particle A ($v_B / v_A$)?
Track Geometry: Two particles A and B move along concentric circular paths of radius $R_A = 1m$ and $R_B = 2m$ respectively, fixed on a rotating rigid platform turning at angular speed $\omega = 3\text{ rad/s}$.
What is the ratio of linear speed of particle B to that of particle A ($v_B / v_A$)?
(A)
0.5
(B)
1.0
(C)
2.0
(D)
4.0
Q8
A solid cylinder of mass $M = 2kg$ and radius $R = 0.2m$ rolls without slipping on a flat horizontal floor at center of mass speed $v = 4m/s$.Calculate the total kinetic energy of the rolling cylinder.
A solid cylinder of mass $M = 2kg$ and radius $R = 0.2m$ rolls without slipping on a flat horizontal floor at center of mass speed $v = 4m/s$.
Calculate the total kinetic energy of the rolling cylinder.
(A)
16 J
(B)
24 J
(C)
32 J
(D)
48 J
Q9
[ Turntable 1: I₁ = 2 kg m², ω₁ = 10 rad/s ] + [ Stationary Disc 2: I₂ = 3 kg m², ω₂ = 0 ] ---> [ Combined System: I₁ + I₂, ω = ? ]A horizontal turntable of moment of inertia $I_1 = 2\text{ kg m}^2$ rotates freely at $\omega_1 = 10\text{ rad/s}$. A non-rotating disc of moment of inertia $I_2 = 3\text{ kg m}^2$ is gently dropped coaxially onto it. What is their final common angular speed?
[ Turntable 1: I₁ = 2 kg m², ω₁ = 10 rad/s ] + [ Stationary Disc 2: I₂ = 3 kg m², ω₂ = 0 ] ---> [ Combined System: I₁ + I₂, ω = ? ]
A horizontal turntable of moment of inertia $I_1 = 2\text{ kg m}^2$ rotates freely at $\omega_1 = 10\text{ rad/s}$. A non-rotating disc of moment of inertia $I_2 = 3\text{ kg m}^2$ is gently dropped coaxially onto it. What is their final common angular speed?
(A)
2 rad/s
(B)
4 rad/s
(C)
5 rad/s
(D)
6 rad/s
Q10
Rod Orientations: Axis 1 passes through center of mass perpendicular to length ($I_{cm}$). Axis 2 passes through one end perpendicular to length ($I_{end}$).For a uniform thin rod, what is the ratio of its moment of inertia $I_{cm}$ to $I_{end}$?
Rod Orientations: Axis 1 passes through center of mass perpendicular to length ($I_{cm}$). Axis 2 passes through one end perpendicular to length ($I_{end}$).
For a uniform thin rod, what is the ratio of its moment of inertia $I_{cm}$ to $I_{end}$?
(A)
$1 : 4$
(B)
$1 : 3$
(C)
$1 : 2$
(D)
$1 : 12$
Q11
Consider a solid uniform sphere of radius $R$. We wish to determine its radius of gyration $k$ about a axis tangent to its outer surface.Express the radius of gyration $k$ in terms of $R$.
Consider a solid uniform sphere of radius $R$. We wish to determine its radius of gyration $k$ about a axis tangent to its outer surface.
Express the radius of gyration $k$ in terms of $R$.
(A)
$\sqrt{\frac{2}{5}} R$
(B)
$\sqrt{\frac{3}{5}} R$
(C)
$\sqrt{\frac{7}{5}} R$
(D)
$\frac{7}{5} R$
Q12
Timing Interval: Initial angular velocity $\omega_0 = 10\text{ rad/s}$. Final angular velocity $\omega = 0\text{ rad/s}$. Stopping time $t = 5\text{ s}$.A rotating wheel is brought to rest by a uniform braking torque in 5 s. What is the magnitude of its angular acceleration?
Timing Interval: Initial angular velocity $\omega_0 = 10\text{ rad/s}$. Final angular velocity $\omega = 0\text{ rad/s}$. Stopping time $t = 5\text{ s}$.
A rotating wheel is brought to rest by a uniform braking torque in 5 s. What is the magnitude of its angular acceleration?
(A)
$1\text{ rad/s}^2$
(B)
$2\text{ rad/s}^2$
(C)
$4\text{ rad/s}^2$
(D)
$5\text{ rad/s}^2$
Q13
Body Shape Factor ($k^2/R^2$) Acceleration Formula Ring 1.0 $a = \frac{g \sin\theta}{1 + k^2/R^2}$ Disc 0.5 $a = \frac{g \sin\theta}{1 + k^2/R^2}$ Solid Sphere 0.4 $a = \frac{g \sin\theta}{1 + k^2/R^2}$
Three bodies (a ring, a disc, and a solid sphere) of equal mass and radius are released simultaneously from rest from the top of an inclined plane. Which object reaches the bottom first?
| Body | Shape Factor ($k^2/R^2$) | Acceleration Formula |
|---|---|---|
| Ring | 1.0 | $a = \frac{g \sin\theta}{1 + k^2/R^2}$ |
| Disc | 0.5 | $a = \frac{g \sin\theta}{1 + k^2/R^2}$ |
| Solid Sphere | 0.4 | $a = \frac{g \sin\theta}{1 + k^2/R^2}$ |
Three bodies (a ring, a disc, and a solid sphere) of equal mass and radius are released simultaneously from rest from the top of an inclined plane. Which object reaches the bottom first?
(A)
Ring
(B)
Disc
(C)
Solid Sphere
(D)
All reach at the same time
Q14
A constant torque of $\tau = 20\text{ N m}$ is applied to rotate a flywheel through an angular displacement of 5 full revolutions.Calculate the total work done by the applied torque.
A constant torque of $\tau = 20\text{ N m}$ is applied to rotate a flywheel through an angular displacement of 5 full revolutions.
Calculate the total work done by the applied torque.
(A)
100 J
(B)
$100\pi\text{ J}$
(C)
$200\pi\text{ J}$
(D)
$400\pi\text{ J}$
Q15
Plane Lamina Setup: A thin flat lamina lies in the xy-plane. Its moments of inertia about the $x$-axis and $y$-axis are $I_x = 4\text{ kg m}^2$ and $I_y = 6\text{ kg m}^2$.Using the Perpendicular Axes Theorem, calculate its moment of inertia $I_z$ about the $z$-axis perpendicular to the lamina plane.
Plane Lamina Setup: A thin flat lamina lies in the xy-plane. Its moments of inertia about the $x$-axis and $y$-axis are $I_x = 4\text{ kg m}^2$ and $I_y = 6\text{ kg m}^2$.
Using the Perpendicular Axes Theorem, calculate its moment of inertia $I_z$ about the $z$-axis perpendicular to the lamina plane.
(A)
$2\text{ kg m}^2$
(B)
$5\text{ kg m}^2$
(C)
$10\text{ kg m}^2$
(D)
$24\text{ kg m}^2$
Q16
A particle of mass $m = 2kg$ moves with a constant velocity $v = 5m/s$ along the horizontal line $y = 3m$ in the xy-plane.Find the magnitude of the angular momentum of the particle about the origin.
A particle of mass $m = 2kg$ moves with a constant velocity $v = 5m/s$ along the horizontal line $y = 3m$ in the xy-plane.
Find the magnitude of the angular momentum of the particle about the origin.
(A)
$10\text{ kg m}^2/\text{s}$
(B)
$15\text{ kg m}^2/\text{s}$
(C)
$30\text{ kg m}^2/\text{s}$
(D)
$60\text{ kg m}^2/\text{s}$
Q17
Thin Cylindrical Shell (Hollow): I_hollow = M R² vs Solid Cylinder: I_solid = (1/2) M R²What is the ratio of moment of inertia of a thin hollow cylinder to that of a solid cylinder of the same mass $M$ and radius $R$ about their central symmetry axis?
Thin Cylindrical Shell (Hollow): I_hollow = M R² vs Solid Cylinder: I_solid = (1/2) M R²
What is the ratio of moment of inertia of a thin hollow cylinder to that of a solid cylinder of the same mass $M$ and radius $R$ about their central symmetry axis?
(A)
$1 : 2$
(B)
$2 : 1$
(C)
$1 : 1$
(D)
$4 : 1$
Q18
A body undergoing pure rotation possesses rotational kinetic energy $E = 100\text{ J}$ and angular momentum $L = 20\text{ J s}$.Determine the moment of inertia of the body about its axis of rotation.
A body undergoing pure rotation possesses rotational kinetic energy $E = 100\text{ J}$ and angular momentum $L = 20\text{ J s}$.
Determine the moment of inertia of the body about its axis of rotation.
(A)
$1\text{ kg m}^2$
(B)
$2\text{ kg m}^2$
(C)
$4\text{ kg m}^2$
(D)
$5\text{ kg m}^2$
Q19
Time Interval Initial Speed Acceleration Displacement Formula 1st second ($t=0$ to 1 s) $\omega_0 = 0$ $\alpha$ $\theta_1 = \frac{1}{2} \alpha (1)^2$ 2nd second ($t=1$ to 2 s) $\omega_1 = \alpha$ $\alpha$ $\theta_2 = \frac{1}{2} \alpha (2)^2 - \theta_1$
A wheel starts from rest and rotates with uniform angular acceleration. Find the ratio of angular displacements $\theta_1 : \theta_2$ covered in the 1st second and the 2nd second respectively.
| Time Interval | Initial Speed | Acceleration | Displacement Formula |
|---|---|---|---|
| 1st second ($t=0$ to 1 s) | $\omega_0 = 0$ | $\alpha$ | $\theta_1 = \frac{1}{2} \alpha (1)^2$ |
| 2nd second ($t=1$ to 2 s) | $\omega_1 = \alpha$ | $\alpha$ | $\theta_2 = \frac{1}{2} \alpha (2)^2 - \theta_1$ |
A wheel starts from rest and rotates with uniform angular acceleration. Find the ratio of angular displacements $\theta_1 : \theta_2$ covered in the 1st second and the 2nd second respectively.
(A)
$1 : 2$
(B)
$1 : 3$
(C)
$1 : 4$
(D)
$2 : 3$
Q20
Cutout Geometry: A uniform disc of mass $M = 6kg$ and radius $R = 1m$. A circular hole of radius $r = 0.5m$ is punched out such that its center is at distance $d = 0.5m$ from the disc's center.Calculate the moment of inertia of the remaining portion about the axis through the original disc's center perpendicular to its plane.
Cutout Geometry: A uniform disc of mass $M = 6kg$ and radius $R = 1m$. A circular hole of radius $r = 0.5m$ is punched out such that its center is at distance $d = 0.5m$ from the disc's center.
Calculate the moment of inertia of the remaining portion about the axis through the original disc's center perpendicular to its plane.
(A)
$1.5\text{ kg m}^2$
(B)
$2.4375\text{ kg m}^2$
(C)
$2.75\text{ kg m}^2$
(D)
$3.0\text{ kg m}^2$

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