Question

an ideal pendulum oscillates in vacuum between two extreme positions A and B.
If it goes from position A to position B and then returns from position B to mean position C in 3 s, then it will complete 3.5 oscillations in what time.
PLZZ HELP!

Answer 1

Travelling time from A to B to C is 3 second.

For one complete oscillations A to B to A.

We know system is in vacuum,

Hence, time taken B to C will be equal to C to A.

For .75 oscillations time is 3 second

Hence for 1 oscillations time will be $\frac{4}{3} *3=4$ sec.

So, for 3.5 oscillations time will be $3.5*4$

                           = 14 second

Answer 2

A~B~C =3s

In vacuum,

B~C = C~A

A~C = C~A = B~C = 1s

Therefore, one oscillation = 4s

So, 3.5 oscillations = 4*3.5

=4 * 35/10

=14s

For 3.5 oscillations, time taken =14s