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Simple Harmonic Motion question

2022 · 27 Jun · Shift 2 · Q54
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  5. /2022 · 27 Jun · Shift 2 · Q54

Simple Harmonic Motion question

2022 · 27 Jun · Shift 2 · Q54

JEE MainPhysicsSimple Harmonic MotionMCQ+4 / −1
The equation of a particle executing simple harmonic motion is given by x=sin⁡π(t+13)mx = \sin \pi \left( {t + {1 \over 3}} \right)mx=sinπ(t+31​)m. At t = 1s, the speed of particle will be (Given : π\piπ = 3.14)
  1. A
    0 cm s −-− 1
  2. B
    157 cm s −-− 1
  3. C
    272 cm s −-− 1
  4. D
    314 cm s −-− 1
View written solutionFree

Correct answer: B

  1. Given equation of SHM

    x=sin⁡[π(t+13)] mx=\sin\left[\pi\left(t+\frac13\right)\right] \text{ m}x=sin[π(t+31​)] m

    This is of the form: x=Asin⁡(ωt+ϕ)x=A\sin(\omega t+\phi)x=Asin(ωt+ϕ)

    So, A=1 m,ω=π rad s−1A=1\text{ m}, \qquad \omega=\pi\text{ rad s}^{-1}A=1 m,ω=π rad s−1

  2. Find velocity equation

    Velocity is: v=dxdtv=\frac{dx}{dt}v=dtdx​

    Differentiate: v=πcos⁡[π(t+13)] m s−1v=\pi\cos\left[\pi\left(t+\frac13\right)\right] \text{ m s}^{-1}v=πcos[π(t+31​)] m s−1

  3. Evaluate at t=1 t=1\,t=1s

    v=πcos⁡[π(1+13)]v=\pi\cos\left[\pi\left(1+\frac13\right)\right]v=πcos[π(1+31​)] =πcos⁡(4π3)=\pi\cos\left(\frac{4\pi}{3}\right)=πcos(34π​)

    Now, cos⁡(4π3)=−12\cos\left(\frac{4\pi}{3}\right)= -\frac12cos(34π​)=−21​

    Hence, v=π(−12)=−π2 m s−1v=\pi\left(-\frac12\right)=-\frac{\pi}{2}\text{ m s}^{-1}v=π(−21​)=−2π​ m s−1

  4. Find speed

    Speed is magnitude of velocity: ∣v∣=π2 m s−1|v|=\frac{\pi}{2}\text{ m s}^{-1}∣v∣=2π​ m s−1

    Using π=3.14\pi=3.14π=3.14, ∣v∣=3.142=1.57 m s−1|v|=\frac{3.14}{2}=1.57\text{ m s}^{-1}∣v∣=23.14​=1.57 m s−1

  5. Convert to cm/s

    1.57 m s−1=157 cm s−11.57\text{ m s}^{-1}=157\text{ cm s}^{-1}1.57 m s−1=157 cm s−1

  6. Match with options

    157 cm s−1\boxed{157\text{ cm s}^{-1}}157 cm s−1​

    So the correct option is B.

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