Solving the Dog's Displacement: Vectors & Magnitude

[nadong2dong]

Homework Statement

A lost dog travels 30 degrees south of west for 450m. He then smells some food and sprints at 20 degrees east of north for 600m.

Homework Equations

a) Draw each vector. Label the magnitude and thetas.
b)Calculate the vector components
c) calculate the magnitude of the dog's displacement.

The Attempt at a Solution

a) I am confused with the second part of the question. Should i use the angle "20degrees" as the theta? or 70 ?
b) first part
-450cos30 = -389.7
-450sin30 = -225
second part ( confused with this part, i used 70 degrees, instead of 20)
600cos70 = 205.2
600sin70= 563.816
c) -389.7+ 205.2 = -184.5 <<<<< X component
-225 + 563.8 = 338.816 <<<<<<< Y component

Square root[ (-184.5)^2 + (338.816)^2 ] = 385.8 m <<< the magnitude of the dogs displacement.

 

[grzz]

You can use either angle 20 or angle 70. Then you have to use cos20 for the vertical component BUT sin70 for the same component.