Given:
initial angular speed,
= 21.5 rad/s
final angular speed,
= 28.0 rad/s
time, t = 3.50 s
Solution:
Angular acceleration can be defined as the time rate of change of angular velocity and is given by:

Now, putting the given values in the above formula:


Therefore, angular acceleration is:

Explanation:
Could you also show the diagram
Answer: 
Explanation:
Given
Length of the race track 
the radius of curvature of the track 
time taken to run on track is 
Speed of runner is

Centripetal acceleration is

Answer:
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Bohr explained that the electron revolve around a orbit of fixed energy level that Rutherford fails to explain !!!