Question

A jogger runs 140 m due west, then changes direction for the second leg of her run. At the end of the run, she is 374 m away from the starting point at an angle of 20o north of west. What were the length and direction of her second displacement?

Answer 1

Answer:

The length of her second displacement = 247.12 m.

The direction of her second displacement = 31.24° from west.

Step-by-step explanation:

As per the question,

From the figure as drawn below,

Let the starting point be O. After running 140 m due west, she reached at point A.

∴ OA = 140 m

And At the end of the run, she is 374 m away from the starting point at an angle of 20° north of west.

∴ OP = 374 m

We have to find the distance AP = x.

By using the cosine rule in triangle OAP

$cos \theta = \frac{OA^{2}+OP^{2}-AP^{2}}{2\times OA\times OP}$

After putting the given value, we get

$cos 20= \frac{140^{2}+374^{2}-x^{2}}{2\times 140\times 374}$

$x^{2}=140^{2}+374^{2} - 2\times 140\times 374\times cos 20$

  ∴ x = 247.12 m  

Hence,the length of her second displacement = 247.12 m.

Again,

By using the cosine rule in triangle OAP, we get

$cos \alpha = \frac{OA^{2}+AP^{2}-OP^{2}}{2\times OA\times AP}$

After putting the given value, we get

$cos \alpha = \frac{140^{2}+247.12^{2}-374^{2}}{2\times 140\times 247.12}$

∴ α = 148.759°

Hence, the  direction of her second displacement = 180° - α = 180° - 148.759 = 31.24° from west.