A particle is moving eastwards with veloci

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A particle is moving eastwards with velocity of $5\,m/s$. In $10 \,sec$ the velocity changes to $5 \,m/s$ northwards. The average acceleration in this time is

A

Zero

B

$\frac{1}{{\sqrt 2 }}\,\,m{\rm{/}}{s^{\rm{2}}}$ toward north-west

C

$\frac{1}{{\sqrt 2 }}\,\,m{\rm{/}}{s^{\rm{2}}}$ toward north-east

D

$\frac{1}{2}\,\,m{\rm{/}}{s^{\rm{2}}}$toward north-west

A particle is moving eastwards with velocity of $5\,m/s$. In $10 \,sec$ the velocity changes to $5 \,m/s$ northwards. The average acceleration in this time is

$\Delta \vec \upsilon = {\vec \upsilon _2} - {\vec \upsilon _1}$$ = \sqrt {\upsilon _1^2 + \upsilon _2^2 - 2{\upsilon _1}{\upsilon _2}\,\,\cos {{90}^o}} $$ = \sqrt {{5^2} + {5^2}} = 5\sqrt 2 $

Average acceleration

$ = \frac{{\Delta \upsilon }}{{\Delta t}} = \frac{{5\sqrt 2 }}{{10}} = \frac{1}{{\sqrt 2 }}\,\,{\rm{m/}}{{\rm{s}}^{\rm{2}}}$

Directed toward north-west   (As clear from the figure).