MCQEasyJEE 2023Simple Harmonic Motion (SHM)

JEE Physics 2023 Question with Solution

For a periodic motion represented by the equation y=sinωt+cosωty = \sin \omega t + \cos \omega t, the amplitude of the motion is:

  • A

    0.50.5

  • B

    11

  • C

    22

  • D

    2\sqrt{2}

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: y=sinωt+cosωty = \sin \omega t + \cos \omega t

Find: The amplitude of the motion.

For the form

y=Asin(ωt)+Bcos(ωt)y = A \sin(\omega t) + B \cos(\omega t)

the amplitude is

A2+B2\sqrt{A^2 + B^2}

Here, A=1A = 1 and B=1B = 1.

So,

Amplitude=(1)2+(1)2=2\text{Amplitude} = \sqrt{(1)^2 + (1)^2} = \sqrt{2}

Therefore, the amplitude is 2\sqrt{2}. Hence, the correct option is D.

The solution states option A, but the worked result clearly gives 2\sqrt{2}, which matches option D.

Common mistakes

  • Taking the amplitude as A+B=2A + B = 2 is incorrect because the resultant amplitude for Asin(ωt)+Bcos(ωt)A \sin(\omega t) + B \cos(\omega t) is not the arithmetic sum. Use A2+B2\sqrt{A^2 + B^2} instead.

  • Assuming the amplitude is 11 by looking at the coefficients separately is wrong because both sine and cosine terms contribute together to the resultant SHM. Combine them using the standard formula.

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