Discussion
A body starts moving from the origin along a straight line at a speed of 20 kmh-1 for 1 hour. Then it turns perpendicular to its path and moves with the same velocity for 30 minutes. Then the magnitude of its displacement is
Answer: C
The displacement is \(10\sqrt{5}\) km.
In the first hour the body covers \(20 \times 1 = 20\) km. It then turns through a right angle and moves for half an hour at the same speed, covering \(20 \times 0.5 = 10\) km.
\[ \begin{aligned} d &= \sqrt{20^{2} + 10^{2}} = \sqrt{500} \\ &= 10\sqrt{5} \text{ km} \end{aligned} \]
30 km would be the distance travelled, not the displacement, and 20 km or 10 km are the two legs on their own.
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