1. ## relative displacement

port A is 80 km due north of port B. the sailing time from A to B is 5 hours. if the velocity of the current west is 12 km hr^-1 find the velocity with which the ferry should head in order to complete the journey in the scheduled time

i have came up with only 1 equation. 80/vcosa =5 im now trying to find another equation with the current velocity in it and solve these 2 equations

2. ## Re: relative displacement

sketch a vector diagram ...

3. ## Re: relative displacement

If you multiply both sides of that equation by v cos(a) you get 5vcos(a)= 80, an equation for the vertical distance traveled. Set up a similar equation for the horizontal distance traveled. If you want to end up at port B, the horizontal distance traveled must be 0.

4. ## Re: relative displacement

so i did vsina-12=0 because horizontal distance traveled is 0 and than i subbed in v=80/5cos a and got 36.87 degrees

5. ## Re: relative displacement

Originally Posted by markosheehan
so i did vsina-12=0 because horizontal distance traveled is 0 and than i subbed in v=80/5cos a and got 36.87 degrees
36.87 degrees relative to what?

Velocity is direction & speed ... what speed should the ferry make good through the water?