Homework Help: vectors

Posted by Molly on Thursday, February 7, 2013 at 6:27pm.

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.

vectors - Steve, Thursday, February 7, 2013 at 11:42pm
If A starts at time 0, and B starts at time k,

(6+8t)i + (10-2t)j = (8+4(t-k-1/2))i + (5+(t-k-1/2))j

so,

6+8t = 8+4(t-k-1/2)
10-2t = 5+t-k-1/2

(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)

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