A particle is moving eastwards with a velocity of $5\; ms^{-1}$. In $10 \;s$ the velocity changes to $5\;ms^{-1}$ northwardas. The average acceleration in this time is:

Question

( A ) $\frac{1}{2} ms^{-2}$ towards north-west
( B ) $\frac{1}{2} ms^{-2}$ towards north
( C ) zero
( D ) $\frac{1}{\sqrt{2}} ms^{-2}$ towards north-east