Q: A car is moving eastwards with velocity 10 m/s. In 20 sec, the velocity changes to 10 m/s northwards. The average acceleration in this time:
(A)1/√2 m s-2 towards N-W
(B)1/√2 ms-2 towards N-E
(C) 1/2 m s-2 towards N-W
(D) 1/2 ms-2 towards N
Solution: The change in velocity is
$ \displaystyle \vec{\Delta v} = \vec{v_2}-\vec{v_1}$
$ \displaystyle = 10\hat{j}-10\hat{i}$
$ \displaystyle \Delta v = 10\sqrt{2} $ and directed due N – W
Average acceleration = Δv ⁄Δt = 10√2/20
= 1/√2 ms-2 and directed due N-W
Ans: (A)