# Question about 2 ships - vectors?

1. Sep 6, 2011

### Star Forger

1. The problem statement, all variables and given/known data

Ships A and B leave port together. For the next two hours, ship A travels at 35 mph in a direction 20° west of north while the ship B travels 10° east of north at 40 mph.

(a) What is the distance between the two ships two hours after they depart (in miles)?

(b) What is the speed of ship A as seen by ship B (in mph)?

2. Relevant equations

3. The attempt at a solution

I have no idea how to approach this problem. I believe it is vectors, however as I said I'm not sure. Any help would be greatly appreciated.

2. Sep 6, 2011

### iRaid

Start by drawing 2 vectors from one point, lets say (0,0)
-One vector will go at a 20° angle to the west (of north) and the other will go 10° east (of north)
-Since it's 2 hours you can make the vector length double (70 and 80).
-You will end up have 1 angle, 2 sides
-You can now use the law of cosines to solve

I believe this is correct, if not someone will correct me :p

Edit: that's part A.

3. Sep 6, 2011

### Star Forger

Thank you, that made a lot of sense and I calculated part A correct. How would I calculate part B though? What does speed as seen by the other mean?

4. Sep 7, 2011

### SteamKing

Staff Emeritus
Pretend you were standing on boat B watching boat A. If both boats were travelling in tje same direction at the same speed, boat A would appear stationary to someone on boat B.