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Simple Harmonic Motion question

2022 · 28 Jun · Shift 1 · Q60
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  5. /2022 · 28 Jun · Shift 1 · Q60

Simple Harmonic Motion question

2022 · 28 Jun · Shift 1 · Q60

JEE MainPhysicsSimple Harmonic MotionNumerical+4 / −1
A pendulum is suspended by a string of length 250 cm. The mass of the bob of the pendulum is 200 g. The bob is pulled aside until the string is at 60 ∘^\circ∘ with vertical as shown in the figure. After releasing the bob, the maximum velocity attained by the bob will be ‾\underline{\hspace{2cm}}​ ms −-− 1. (if g = 10 m/s2) JEE Main 2022 (Online) 28th June Morning Shift Physics - Simple Harmonic Motion Question 63 English
Numerical answer
View written solutionFree

Correct answer: 5

  1. Given data

    • Length of pendulum: L=250 cm=2.5 mL = 250\text{ cm} = 2.5\text{ m}L=250 cm=2.5 m
    • Mass of bob: m=200 g=0.2 kgm = 200\text{ g} = 0.2\text{ kg}m=200 g=0.2 kg
    • Angular displacement: θ=60∘\theta = 60^\circθ=60∘
    • Acceleration due to gravity: g=10 m/s2g = 10\text{ m/s}^2g=10 m/s2
  2. Concept used The bob is released from rest at 60∘60^\circ60∘ from the vertical. Its maximum speed occurs at the lowest point.

    We use conservation of mechanical energy: mgh=12mv2mgh = \frac{1}{2}mv^2mgh=21​mv2

  3. Find the vertical height fallen by the bob For a pendulum displaced by angle θ\thetaθ from vertical, the rise in height above the lowest point is: h=L(1−cos⁡θ)h = L(1-\cos\theta)h=L(1−cosθ)

    Substituting values: h=2.5(1−cos⁡60∘)h = 2.5(1-\cos60^\circ)h=2.5(1−cos60∘) cos⁡60∘=12\cos60^\circ = \frac{1}{2}cos60∘=21​ h=2.5(1−12)=2.5×0.5=1.25 mh = 2.5\left(1-\frac{1}{2}\right) = 2.5 \times 0.5 = 1.25\text{ m}h=2.5(1−21​)=2.5×0.5=1.25 m

  4. Apply energy conservation mg(1.25)=12mv2mg(1.25) = \frac{1}{2}mv^2mg(1.25)=21​mv2

    Mass cancels out: g(1.25)=v22g(1.25) = \frac{v^2}{2}g(1.25)=2v2​

    10×1.25=v2210 \times 1.25 = \frac{v^2}{2}10×1.25=2v2​ 12.5=v2212.5 = \frac{v^2}{2}12.5=2v2​ v2=25v^2 = 25v2=25 v=5 m/sv = 5\text{ m/s}v=5 m/s

  5. Final answer The maximum velocity attained by the bob is: 5\boxed{5}5​

  6. Comparison with stored answer Stored correct answer = 555

    This matches the derived answer.

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