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High School Physics BLOG - online class notes

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September 18, 2019

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

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.

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.

Time period of A = Ta
and Time period of B = Tb
Ta / Tb =√(1/4) = ½
So Tb = 2 Ta

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.

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

Question Set – Physics Problems for grade 9

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