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3-2.Motion in Plane
normal
A stone is tied to a string of length $L$ is whirled in a vertical circle with the other end of the string at the centre. At a certain instant of time, the stone is at its lowest position and has a speed $u.$ The magnitude of the change in its velocity as it reaches a position where the string is horizontal is
A
$u-\sqrt{u^{2}-2 g l}$
B
$\sqrt {2gL}$
C
$\sqrt {{u^2} - gL}$
D
$\sqrt {2({u^2} - gL)} $
Solution
$\left|\vec{v}-\vec{u}\right|$
$=|\sqrt{\mathrm{u}^{2}-2 \mathrm{g}} \mathrm{L} \hat{\mathrm{j}}-u \hat{\mathrm{i}}|$
$=\sqrt{(\sqrt{\mathrm{u}^{2}-2 \mathrm{g} \mathrm{L}})^{2}+u^{2}}$
$=\sqrt{2\left(\mathrm{u}^{2}-\mathrm{gL}\right)}$
Standard 11
Physics
