28. A body is moving with velocity 30 m/s towards east. After 10 seconds its velocity becomes 40 m/s towards north. The average acceleration of the body is

28. A body is moving with velocity 30 m/s towards east. After 10 seconds its velocity becomes 40 m/s towards north. The average acceleration of the body is

(a) 1  \(m/s^2\)

(b) 7  \(m/s^2\)

(c) 6  \(m/s^2\)

(d) 5  \(m/s^2\)

Answer :  (d) 5  \(m/s^2\)

\( \vec{a}_{avg} = \)\(\frac{\vec{v}_2 - \vec{v}_1}{t_2 - t_1} \)

= \( \frac{(40\hat{j}) - (30\hat{i})}{10} \)

= \( \frac{-30\hat{i} + 40\hat{j}}{10} \)

\( = -3\hat{i} + 4\hat{j} \)

\( |\vec{a}_{avg}| = \sqrt{(-3)^2 + 4^2} \)

= 5 \( m/s^2 \)