First slide

Kinematics of rotational motion about fixed axis

Question

A disc of radius r = 20 cm is rotating about its axis with an angular speed of 20 rad/s. It is gently placed on a horizontal surface which is perfectly frictionless (see fig. 1).
What is the linear speed of a point B on the disc ?

Easy

A

1 m/s
B

2 m/s
C

3 m/s
D

4 m/s

Solution

When the disc is placed on horizontal frictionless surface, it will not roll on the surface but it will simply keep on rotating at point A, where it is placed.
We know that v = ωr, where ω = angular speed
∴ Linear speed at B = 20 × 0⋅2 = 4 m/s

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