Select the correct answers of the following questions:

1. The angular speed in rad/hours for daily rotation of our earth is

2π

4π

π/6

π/12

Solution

In the complete rotation, the earth traverses an angle = 2π rad

Time taken in a complete rotation = 24 hrs Therefore, angular speed

2. Linear acceleration is a = rα when θ is

0o

180o

360o

90o

Explanation: Relation of linear and angular acceleration is

Its magnitude is rasinα. For α = 90° sin90° = 1, therefore, a = rα.

3. What is moment of inertia of a sphere

MR2

½ MR2

2/5 MR2

½ M2R

4. Artificial satellite moves around

Moon

Sun

Star

Earth

5. A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a horizontal plane. It follows

Linear momentum is constant

Velocity is constant

It moves in a circular path

None of these

6. A body moving along a circular path with constant speed has

Constant acceleration

Constant retardation

Variable acceleration

Variable speed and constant acceleration

Explanation: When a body is moving in circular path, its direction changes at every point. Since change in direction is accompanied by a change in the acceleration on every point, therefore, the body moving in a circle has variable acceleration.

7. Which one is constant for a satellite in the orbit?

Velocity

K.E

Angular Momentum

P.E

Explanation: Since angular momentum, L = r x p.

A satellite has constant mass and speed, therefore, its linear momentum p is constant. Similarly, the radius r is also constant. Therefore, angular momentum L is constant.

8. If earth suddenly stops rotating the value of ‘g’ at equator would

Decreases

Remains constant

Increases

Becomes zero

Explanation: When the earth stops its rotation about its own axis, the centrifugal force is also stopped. This increases the gravitational force. (Note that the centrifugal force is more on equator than the poles).

9. If a solid sphere and cylinder of mass and density rotate about their own axis, the moment of inertia will be greater for

Solid sphere

Solid cylinder

Both

Equal both