A simple pendulum is hollow from within and its time period is T. how is the time period of pendulum affected when: a) ¼ of Bob is filled with mercury
b)¾ of Bob is filled with Mercury
c) the bob is completely filled with Mercury
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The period of a pendulum is independent of the mass of the bob so whether it's empty or filled with something, the period remains the same.

Explanation:

The question says that, "After how long does a mobile acquire a speed of 30 m / s, if it starts from rest and its acceleration is 3 m / s*2"

Initial speed is 0

Final speed is 30 m/s

Acceleration a = 3 m/s²

It is required to find time when it acquire a speed of 30 m/s. Using equation of kinematics as :

So, after 10 seconds it will acquire a speed of 30 m/s.