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Simple Harmonic Motion question

2021 · 26 Aug · Shift 2 · Q68
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Simple Harmonic Motion question

2021 · 26 Aug · Shift 2 · Q68

JEE MainPhysicsSimple Harmonic MotionNumerical+4 / −1
Two simple harmonic motions are represented by the equations x1=5sin⁡(2πt+π4){x_1} = 5\sin \left( {2\pi t + {\pi \over 4}} \right)x1​=5sin(2πt+4π​) and x2=52(sin⁡2πt+cos⁡2πt){x_2} = 5\sqrt 2 (\sin 2\pi t + \cos 2\pi t)x2​=52​(sin2πt+cos2πt). The amplitude of second motion is ................ times the amplitude in first motion.
Numerical answer
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Correct answer: 2

  1. Identify the amplitude of the first SHM

    The first motion is x1=5sin⁡(2πt+π4).x_1 = 5\sin\left(2\pi t + \frac{\pi}{4}\right).x1​=5sin(2πt+4π​).

    This is already in the standard SHM form x=Asin⁡(ωt+ϕ),x = A\sin(\omega t + \phi),x=Asin(ωt+ϕ), so its amplitude is A1=5.A_1 = 5.A1​=5.

  2. Rewrite the second SHM in standard form

    The second motion is x2=52(sin⁡2πt+cos⁡2πt).x_2 = 5\sqrt{2}(\sin 2\pi t + \cos 2\pi t).x2​=52​(sin2πt+cos2πt).

    Use the identity sin⁡θ+cos⁡θ=2sin⁡(θ+π4).\sin\theta + \cos\theta = \sqrt{2}\sin\left(\theta + \frac{\pi}{4}\right).sinθ+cosθ=2​sin(θ+4π​).

    Therefore, x2=52⋅2sin⁡(2πt+π4).x_2 = 5\sqrt{2}\cdot \sqrt{2}\sin\left(2\pi t + \frac{\pi}{4}\right).x2​=52​⋅2​sin(2πt+4π​).

    So, x2=10sin⁡(2πt+π4).x_2 = 10\sin\left(2\pi t + \frac{\pi}{4}\right).x2​=10sin(2πt+4π​).

    Hence the amplitude of the second motion is A2=10.A_2 = 10.A2​=10.

  3. Find how many times the second amplitude is the first

    A2A1=105=2.\frac{A_2}{A_1} = \frac{10}{5} = 2.A1​A2​​=510​=2.

  4. Final answer

    The amplitude of the second motion is 222 times the amplitude of the first motion.

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