A pendulum bob has a speed of 3ms^-1 at its… - JEE Main 2021 Physics PYQ

JEE Main 2021 — Physics Waves & Oscillations

2021integermedium

A pendulum bob has a speed of $3m{s}^{-1}$ at its lowest position. The pendulum is $50\mathrm{cm}$ long. The speed of bob, when the length makes an angle of $60^{\circ}$ to the vertical will be $(g=10m{s}^{-2})$ ______ $m{s}^{-1}$ .

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Held on 25 Jul 2021 · Verified 6 Jul 2026.

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Solution

JEE Main 2021 Physics, Oscillations — solution figure

Applying work energy theorem:

${w}_{g}+{w}_{T}=\Delta K$

$-mgl(1-\mathrm{cos}60^{\circ})=\frac{1}{2}m{v}^{2}-\frac{1}{2}m{u}^{2}$

${v}^{2}={u}^{2}-2gl(1-\mathrm{cos}60^{\circ})$

${v}^{2}=9-2\times 10\times 0.5(\frac{1}{2})$

${v}^{2}=4$

$v=2m{s}^{-1}$

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