Question

A truck travelling due north at 20 m/s turns west and travels at the same speed. The change in its velocity be

• A. 40 m/s N–W
• B. $20\sqrt{2}$m/s N–W
• C. 40 m/s S–W
• D. $20\sqrt{2}$ m/s S–W

Answer 1

Answer: (D)

$20\sqrt{2}$ m/s S–W

Answer 2

From figure

${\overset{\rightarrow}{v}}_{1} = 20\widehat{j}$ and ${\overset{\rightarrow}{v}}_{2} = - 20\widehat{i}$

$\Delta\overset{\rightarrow}{v} = {\overset{\rightarrow}{v}}_{2} - {\overset{\rightarrow}{v}}_{1} = - 20(\widehat{i} + \widehat{j})$

$|\Delta\overset{\rightarrow}{v}| = 20\sqrt{2}$and direction

$\theta = \tan^{- 1}(1) = 45{^\circ}$ i.e. S–W