Rolling on Inclined Plane - NEET Physics Questions
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Rolling on Inclined Plane

Question 1: moderate

A disk and a sphere of same radius but different masses roll off on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first?

(2016 – I)

1. Disk
2. Sphere
3. Both reach at the same time
4. Depends on their masses
View Answer

Acceleration of a rolling body on an inclined plane is given by $$a = \frac{g sin\theta}{1 + I/(mR^2)}$$. Since the acceleration is independent of mass and depends only on the geometry (moment of inertia factor), the sphere has a smaller inertia factor than the disk, meaning the sphere has a greater acceleration and reaches the bottom first.

Question 2: moderate

The ratio of the accelerations for a solid sphere (mass m and radius R) rolling down an incline of angle $theta$ without slipping and slipping down the incline without rolling is:

(2014)

1. $5 : 7$
2. $2 : 3$
3. $2 : 5$
4. $7 : 5$
View Answer

Acceleration without slipping is $a_1 = \frac{g sin\theta}{1 + I/(mR^2)} = \frac{5}{7}g sin\theta$. Acceleration with pure slipping is $a_2 = g sin\theta$. The ratio $a_1/a_2$ is $5/7$.

Question 3: moderate

Small object of uniform density rolls up a curved surface with an initial velocity $v$. It reaches to a maximum height of $\frac{3v^2}{4g}$ with respect to the initial position. The object is:

(2013)

1. Disc
2. Ring
3. Solid sphere
4. Hollow sphere
View Answer

Using energy conservation, initial kinetic energy equals potential energy at max height: $\frac{1}{2}mv^2 \left(1 + \frac{I}{mR^2}\right) = mgH$. Substituting $H = \frac{3v^2}{4g}$, we get $1 + \frac{I}{mR^2} = 2$, which gives $\frac{I}{mR^2} = 1$. This corresponds to a ring.

Question 4: easy

A solid cylinder and a hollow cylinder, both of the same mass and same external diameter are released from the same height at the same time on an inclined plane. Both roll down without slipping. Which one will reach the bottom first?

(2010 Mains)

1. Both together only when angle of inclination of plane is $45^{\circ}$
2. Both together
3. Hollow cylinder
4. Solid cylinder
View Answer

The acceleration of a rolling body depends on its moment of inertia ratio $I/mR^2$. The solid cylinder has a smaller moment of inertia ratio ($1/2$) compared to the hollow cylinder ($1$), giving it a higher acceleration and causing it to reach the bottom first.

Question 5: easy

A drum of radius R and mass M, rolls down without slipping along an inclined plane of angle $theta$. The frictional force:

(2005)

1. Converts translational energy to rotational energy
2. Dissipates energy as heat
3. Decreases the rotational motion
4. Decreases the rotational and translational motion
View Answer

Static friction provides the necessary torque for rolling without slipping, converting translational kinetic energy into rotational kinetic energy without dissipating mechanical energy.

Question 6: easy

A solid cylinder of mass $M$ and radius $R$ rolls without slipping down an inclined plane of length $L$ and height $h$. What is the speed of its centre of mass when the cylinder reaches its bottom:

(2003)

1. $\sqrt{2gh}$
2. $\sqrt{\frac{3}{4}gh}$
3. $\sqrt{\frac{4}{3}gh}$
4. $\sqrt{4gh}$
View Answer

Using conservation of energy, potential energy equals total kinetic energy: $Mgh = \frac{3}{4}Mv^2$. Solving for velocity gives $v = \sqrt{\frac{4}{3}gh}$.

Question 7: moderate

For a hollow cylinder & a solid cylinder rolling without slipping on an inclined plane, then which of these reaches earlier on the ground:

(2000)

1. Solid cylinder
2. Hollow cylinder
3. Both simultaneously
4. Can't say anything
View Answer

Acceleration of a rolling body is given by $$a = \frac{g \sin\theta}{1 + I/MR^2}$$. Since the solid cylinder has a smaller moment of inertia ratio than the hollow cylinder, its acceleration is greater, so it reaches the bottom first.

Question 8: moderate

A solid sphere, disc and solid cylinder all of the same mass and made of the same material are allowed to roll down (from rest) on the inclined plane, then:

(1993)

1. Solid sphere reaches the bottom first
2. Solid sphere reaches the bottom last
3. Disc will reach the bottom first
4. All reach the bottom at the same time
View Answer

The acceleration on an inclined plane is inversely proportional to $1 + I/MR^2$. Solid sphere has the lowest moment of inertia coefficient ($2/5$), giving it maximum acceleration and shortest time to reach the bottom.

Question 9: moderate

The speed of a homogenous solid sphere after rolling down an inclined plane of vertical height $h$ from rest without sliding is:

(1992)

1. $\sqrt{\frac{10}{7}gh}$
2. $\sqrt{gh}$
3. $\sqrt{\frac{6}{5}gh}$
4. $\sqrt{\frac{4}{3}gh}$
View Answer

Using conservation of mechanical energy: $mgh = \frac{1}{2}mv^2 + \frac{1}{2}I\omega^2$. For a solid sphere ($I = \frac{2}{5}MR^2$), solving yields $v = \sqrt{\frac{10}{7}gh}$.