### Solution to problems – class 9 – Set 1 Q61, Q62, Q63

##### July 7, 2019

## Problem Statement

61) Two simple pendulums *A *and *B *have
equal length, but their bobs weigh 50 gf and l00 gf respectively. What would be
the ratio of their time periods ? Give reason for your answer.

Solution:

Ratio of their time periods would be 1:1.

Time period of simple pendulum is not dependent on the mass of its bob.

62) Two simple pendulums *A *and *B *have
length 1·0m and 4·0 m respectively at a certain place. Which pendulum will make
more oscillations in 1 minute? Explain your answer.

Solution:

Time period of A = T_{a}

and Time period of B = T_{b }T_{a} / T_{b} =√(1/4) = ½

So T_{b} = 2 T_{a }

A will take half of the time taken by B to complete an oscillation.

So obviously pendulum A will make more oscillations in 1 minute.

63)A simple pendulum completes 40 oscillations in one minute. Find its (a) frequency, (b) time period.

Solution:

In 60 seconds it makes 40 oscillations

In 1 sec it makes = 40/60 = 2/3 oscillation

So frequency = 2/3 per second = 0.67 Hz

Time period = 1/frequency = 3/2 = 1.5 seconds