College Physics 3.17 – Reverse addition of vectors

Repeat Problem 3.16 using analytical techniques, but reverse the order of the two legs of the walk and show that you get the same final result. (This problem shows that adding them in reverse order gives the same result—that is, B+A=A+B) Discuss how taking another path to reach the same point might help to overcome an obstacle blocking your other path.

Reverse addition of the two vectors A and B.
Reverse addition of the two vectors A and B.


Consider the right triangle formed by the legs A, B, and R. We know that A is 18 m, B is 25 m, and we are solving for the magnitude of R. We can do this by using the Pythagorean Theorem. That is






So, the distance is about 30.8 meters from the starting point. To solve for the value of the unknown angle, φ, we can use the tangent function. That is 

tan\:\phi =\frac{A}{B}

tan\:\phi =\frac{18\:m}{25\:m}

\phi =tan^{-1}\left(\frac{18}{25}\right)

\phi =35.75^{\circ}

Therefore, the compass angle is 35.75^{\circ} \:West\:of\:North