Rigid Bodies: Translational Motion And Rotational Motion - Practice Questions & MCQ

1. Pure Translational motion-

If each particle of it has same velocity/acceleration at a particular instant of time then A body is said to have pure translational motion.

• Slipping-

It is motion in which  the body slides on a surface without rotation.

Example- Motion of a wheel on a frictionless surface.

Here  friction between the body and surface =f= 0 

Wheel possess only translatory kinetic energy

i.e., -

 

2. Pure rotational motion-

When a body rotates such that its axis of rotation does not move then that body is said to have pure rotational motion.

In pure rotational motion each particle of body has same angular velocity/acceleration about its axis of rotation at a particular instant  of time.

Example- Spinning  of wheel about fixed axis

Here  axis of rotation of a wheel  is fixed.

Here  body possess only rotary kinetic energy.

I.e

Here Rotational angular momentum = 

Where = Moment of inertia about fixed axis of rotation

= angular velocity of rotation

 

Another example- Motion of blades of a fan

 

3. Combined rotation and translation motion

In this type of motion body is having both rotation and translation motion.

• Rolling

 In case of rolling motion a body rotates about a fixed axis, and the axis of rotation also moves.

Example- Rolling of football on ground

Here friction between the body and surface = 

1. Kinetic energy-

Total kinetic energy of body is sum of both translational and rotational kinetic energy.

Using  

 

2. Net Velocity at a point-

                     Where, 

 

           

Angular momentum is always calculated about a particular point.

Net Angular momentum of body is sum of angular momentum due to both translational and rotational motion.

      

Where represents the angular momentum of the body about center of mass and r is the position vector about which we have to calculate the angular momentum.