vectors
posted by Molly .
The position vectors, r km, and the velocity vectors, v km/h, of two boats at a certain time are given by ...
Boat A:at 10:00 am rA=6i+10j vA=8i–2j
Boat B:at 10:30 am rB=8i+5j vB=4i+j
... determine the time at which boat B should head out so that the two boats do collide.

If A starts at time 0, and B starts at time k,
(6+8t)i + (102t)j = (8+4(tk1/2))i + (5+(tk1/2))j
so,
6+8t = 8+4(tk1/2)
102t = 5+tk1/2
(k,t) = (11/8,11/8)
B had to leave at 10:00  1:122:30 = 8:37:30
At t=11/8 = 11:22:30, both boats are at (17,7.25)