A rod of length 20 cm has two beads attached to its ends. The rod with beads starts rotating from rest. If the beads are to have a tangential speed of 20 m/s in 7 s, what is the angular acceleration of the rod to achieve this?

Explanation:

We use the following rotational kinematic equation to calculate the angular acceleration of the rod:

Here is the final angular speed, is the initial angular speed and is the angular acceleration. The rod starts rotating from rest ():

Recall that the angular speed is defined in function of the tangential speed (v) and the radius (r) of the circular motion:

In this case the radius is given by . Replacing (2) in (1):

the answer is b ) square root of 5