A 120, g mass has a velocity vec v = 2hat{i} + 5hat{j},m{s^{ - 1}} at a certain ins

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5.Work, Energy, Power and Collision

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A $120\, g$ mass has a velocity $\vec v = 2\hat i + 5\hat j\,m{s^{ - 1}}$ at a certain instant. Its kinetic energy is .................. $\mathrm{J}$

A

$3$

B

$4$

C

$5$

D

$1.74$

Solution

$\mathrm{K.E}=\frac{1}{2} \mathrm{mv}^{2}$

$=\frac{1}{2} m(\vec{v} . \vec{v})$

$=\frac{1}{2} m(2 \hat{i}+5 \hat{j}) \cdot(2 \hat{i}+5 \hat{j})$

$=\frac{1}{2} \times \frac{120}{1000}(4+25)$

$=1.74 \mathrm{J}$

Standard 11

Physics

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