Q 11-03-013NEETAIPMT 2011Top questionEasy
A body is moving with velocity $30\ \text{m s}^{-1}$ towards east. After $10$ s its velocity becomes $40\ \text{m s}^{-1}$ towards north. The average acceleration of the body is
Answer: (C) $5\ \text{m s}^{-2}$
Concept. Average acceleration $= \dfrac{\Delta\vec v}{\Delta t}$ uses the vector change in velocity.
Step 1. Change. $\Delta\vec v = 40\hat N - 30\hat E$, $|\Delta\vec v| = 50$ m/s.
Step 2. Acceleration. $\dfrac{50}{10} = 5\ \text{m s}^{-2}$. (Subtracting speeds, $40 - 30$, would ignore the turn.)
Answer. $5\ \text{m s}^{-2}$ (Option C).
Solution by Sreeraj P, M.Sc Physics