Simple Harmonic Motion 1 Question 1

1. A pendulum is executing simple harmonic motion and its maximum kinetic energy is K1. If the length of the pendulum is doubled and it performs simple harmonic motion with the same amplitude as in the first case, its maximum kinetic energy is K2. Then

(2019 Main, 11 Jan III)

(a) K2=2K1

(b) K2=K12

(c) K2=K14

(d) K2=K1

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Answer:

Correct Answer: 1. (b)

Solution:

  1. Kinetic energy of a pendulum is maximum at its mean position. Also, maximum kinetic energy of pendulum

Kmax=12mω2a2

where,angular frequency

ω=2πT=2π2πlg or ω=gl or ω2=gl

and a= amplitude.

As amplitude is same in both cases so;

or

Kmaxω2Kmax1l

[g is constant ]

According to given data, K11l

 and K212lK1K2=1/l1/2l=2 or K1=2K2K2=K12



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