Question

A truck travelling due north at 20 m s^–1 turns west and travels with same speed. What are the changes in velocity?

• A. $20\sqrt{2}$m s^–1 south-west
• B. 40 m s^–1 south-west
• C. $20\sqrt{2}$m s^–1 north-west
• D. 40 m s^–1 north-west

Answer 1

Answer: (A)

$20\sqrt{2}$m s^–1 south-west

Answer 2

$\overset{\rightarrow}{v_{1}}$ = 20 m/s due north

$\overset{\rightarrow}{v_{2}}$ = 20 m/s due west

$|\overset{\rightarrow}{v_{2}} - \overset{\rightarrow}{v_{1}}|$ = $\sqrt{v_{1}^{2} + v_{2}^{2} - 2v_{1}v_{2}\cos\theta}$

= $\sqrt{20^{2} + 20^{2} - 0}$ [Qθ = $90^{0}$]= $20\sqrt{2}$ m/s

≡

Direction of $\overset{\rightarrow}{v_{2}} - \overset{\rightarrow}{v_{1}}$ is due South –West