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13. oscillations — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics13. oscillations1 Mark
MCQ
A pendulum bob has a speed of $3\, {m} / {s}$ at its lowest position. The pendulum is $50 \,{cm}$ long. The speed of bob, when the length makes an angle of $60^{\circ}$ to the vertical will be $ .......\,{m} / {s}$ $\left(g=10 \,{m} / {s}^{2}\right)$
  • A
    $1$
  • B
    $20$
  • C
    $40$
  • ✓
    $2$
✓

Answer

Correct option: D.
$2$
d
Applylng work energy theorem

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

$- mgl \left(1-\cos 60^{\circ}\right)=\frac{1}{2} mv ^{2}-\frac{1}{2} mu ^{2}$

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

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

$v ^{2}=4$

$v =2 m / s$

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