Physics 1 Marks Question

False. Explanation: Frictional force acts opposite to the direction of motion of the centre of mass of a body. In the case of rolling, the direction of motion of the centre of mass is backward. Hence, frictional force acts in the forward direction.

True. Explanation: When perfect rolling begins, the frictional force acting at the lowermost point becomes zero. Hence, the work done against friction is also zero.

True.Explanation:
The rolling of a body occurs when a frictional force acts between the body and the surface. This frictional force provides the torque necessary for rolling. In the absence of a frictional force, the body slips from the inclined plane under the effect of its own weight.

False. Explanation: When a body is rolling, its instantaneous acceleration is not equal to zero. It has some value.

True. Explanation: Rolling can be considered as the rotation of a body about an axis passing through the point of contact of the body with the ground. Hence, its instantaneous speed is zero.

Since no external force acts, the centre of mass will stay where it is.

Concentration of mass at the rim increases the moment of inertia and thereby brings uniform motion.

L is conserved. If the earth shrinks, duration of the day decreases.

No, it depends only on the distribution of mass of the body.

The centre of mass (CM) of a rectangular block lies in the middle of the block. When the block is projected less than half of its length (CM being over the table), no net force acts on it. Thus, no net torque acts upon the body.But if the block is projected more than half of its length outside the table (CM being outside the table), gravitational force acts along the CM of the block. This force produces a moment along the edge of the table. This rotates the block, and as a result, it falls down.

While falling a cat stretches its body along with the tail so that its moment of inertia (I) increases. As no external torque acts, L = Iw = constant. As I increases, w decreases and it lands gently on its feet.

The head of a screw is made wide so as to have a greater torque for the applied force.

A ring has a larger moment of inertia because its entire mass is concentrated at the rim at the maximum distance from the axis.

No, angular momentum is dependent on the position vector of the particle, angle between the radius vector and the linear velocity of the particle. So, there may be finite angular momentum along any different point even if it is zero at a particular point. If angular momentum is zero along O but finite along O.

Moment of inertia of a body depends upon:

1. Mass of the body.
2. Shape and size of body.
3. Position of the axis of rotation.
4. Distribution of mass in the body about the axis of rotation.

It lies at the centroid of the triangular lamina, i.e., where the three medians of the triangular lamina intersects.

Cause-Torque. Outcome-Angular momentum.

Rotational analogue of mass is moment of inertia.

For translational equilibrium of a body net force acting on it i.e., the vector sum of all the forces acting on the body must be zero.

Moment of inertia of a sphere is less than that of a cube of same mass.

Torque to rotate is not created by pushing or pulling along its radius.

For rotational equilibrium of a body the vector sum of torques of all the forces acting on the body about the reference point must be zero.

Length of the day reduces as earth shrinks.

Moment of inertia of a body depends on position and orientation of axis of rotation. It also depends on shape, size of the body and also on the distribution of mass of the body about the given axis.

The radial component of a force does not contribute towards torque.

No, because the moment of inertia depends upon the axis of rotation and distribution of mass.

The wheel does not fall as long as the angular momentum remains constant. Due to friction angular momentum changes and when the wheel stops, it comes to unstable equilibrium.

As coefficient of friction is less than the one required for rolling, therefore the sphere will slip i.e., ii will translate and rotate about the centre.

The moment of inertia gives a measure of inertia in rotational motion. So, it is also called rotational inertia.

Rotational analogue of force is torque.

No, the centre of mass of L-shaped rod lies in the region outside of rod.

Yes, A particle in translatory motion always has an angular momentum, unless the point (about which angular momentum is calculated) lies on the line of motion.

Two factors on which centre of mass of a body does not depend.

1. Choice of coordinate system.
2. Rotatory motion of a body.

Weight provides necessary centripetal force at the highest point.

The point of contact of the ladder with the ground is the point about which the ladder can rotate. When the labourer is at the top of the ladder, the lever arm of force is large. So, the turning effect can be large.

No, since torque cannot be applied.

Yes in case cube is uniform in that case center of mass should be inside cube.

No, Angular velocity is not conserved but angular momentum is conserved.

To develop torque with less force being applied.

This is based on the principle of conservation of angular momentum.

No, the centre of mass of a ring lies at its centre.

The body with the smallest moment of inertia will roll down taking the smallest time. Here, the solid sphere has the lowest moment of inertia among all the other bodies. So, it will roll down taking the least time.

Yes, when the body has a uniform mass density.

Concentration of mass at the rim increases the moment of inertia and thereby brings uniform motion.

Yes, it is an example of pure rotation. The axis of rotation passes through the pivot of the pendulum, perpendicular to the plane containing the pendulum.

Decreases in magnitude and remains the same in direction (along the axis).

The tension required to maintain the mass increases with the length of the string.

A pair of equal and opposite forces acting on a body along two different lines of action constitute a couple.

Torque acting on a body is equal to rate of change of angular momentum.

A body is said to be rigid if it does not change its shape and size when external force acts on it.

For having more torque with less force.

The algebraic sum of the moments of masses of various particles of a system about its centre of mass is zero.

For smaller dimensions, they coincide. A rigid body can be balanced by applying a force equal and opposite to its weight at the centre of gravity.

It is more likely to slip when a man stands at the top of the ladder. This is due to the fact that the man's weight will provide an extra torque for the slipping of the ladder.

Some points on the equator of the sphere has got vertical velocity with respect to the direction of motion of the sphere.

Radial component of linear momentum.

Centre of mass of a triangular lamina is at the point of intersection of the is medians.

The moments of inertia will be different on account of different distances.

When the separation between any two masses consistiting does not vary, the body is said to be rigid.

Friction with the surface.

No, it may lie outside the body. In case of semicircular ring, it is at the centre which is outside the ring.

They are of unequal mass. Their masses are in the inverse ratio of the arms of the balance.

Yes in the case when all of particles are on same axis the center of mass would also lie on the same axis.

Only rotational motion.

Angular momentum gained by the bullet provides better accuracy.

No, the moment of inertia greatly depends on the distribution of mass about the axis of rotation.

Radius of gyration of a given body depends upon the choice of rotation axis. However, for a given axis of rotation, the radius of gyration of a body has a fixed value.

To increase moment of inertia with less mass.

Yes, since no external torque acts on the planets.

The stone will move along the tangent at the point of breaking.

In a uniform cube, the mass is more concentrated about a diagonal.