First slide

Motion in a plane

Question

A truck travelling due north at 20 $m s^{- 1}$ turns west and travels with same speed. What is the change in velocity?

Moderate

A

$20 \sqrt{2} m s^{- 1} s o u t h - w e s t$
B

$40 m s^{- 1} s o u t h - w e s t$
C

$20 \sqrt{2} m s^{- 1} n o r t h - w e s t$
D

$40 m s^{- 1} n o r t h - w e s t$

Solution

Change in velocity $|\vec{Δ V}| = |\vec{V_{f}} - \vec{V_{i}}|$
$= |20 (- \hat{i}) - 20 \hat{j}|$
$= \sqrt{{(20)}^{2} + {(20)}^{2}} = 20 \sqrt{2} m / s$ as the diagram shows it's direction is along south west

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