Pure Rotation about an Axis

Q.

The position of axis of rotation of a body is changed so that its moment of inertia decreases by 36%. The % change in its radius of gyration is

1. Decreases by 20%

2. Increases by 20%

3. Decreases by 18%

4. Increases by 18%

Q.

A helicopter is moving to the right at a constant horizontal velocity. It experiences three forces ${\overrightarrow{F}}_{gravitational},{\overrightarrow{F}}_{drag}$ and force on it caused by rotor i.e. ${\overrightarrow{F}}_{rotor}$. Which of the following diagrams can be correct free body diagram representing forces on the helicopter?

1. 

2. 

3. 

4. 

Q. A wheel of radius 1m rolls forward half a revolution on a horizontal ground the magnitude of the displacement of the wheel intially in contact with the ground is

Q. 4. A disc of radius R rotates fro rest about a vertical axis with a constant angular acce. Such that coin placed at the periphery of the disc moves with tangential acc a. If the coefficient of static friction is $ fi d the distance travelled and the time taken before sliding?

Q. If all the points on a rigid body are performing circular motion about a common axis of rotation then one can deduce that the body is undergoing pure rotational motion.

1. True
2. False

Q.

Which of the following is/are necessary and sufficient condition(s) for pure rotation?

1. All particles of the body will move in concentric circles.

2. All particles move in a circle contained in parallel planes.

3. Centre of all the particles of the body lie on a same straight line called the Axis of rotation.

4. Axis of rotation is always perpendicular to the planes of the circles