Relative velocity boat crossing a river

AI Thread Summary
The discussion focuses on a physics problem involving a boat crossing a 240 m wide river with a current. The actual velocity of the boat is calculated to be 13 m/s using the Pythagorean theorem. It takes 48 seconds for the boat to cross the river, resulting in a downstream distance of 576 m. There is a discrepancy noted between the calculated time and the book's answer, which suggests a time of 20 seconds. The consensus is that the book likely misrepresented the relative speeds involved in the problem.
Woolyabyss
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Homework Statement


A boat crosses river, 240 m wide,which flows parallel to the straight banks with velocity
v1 = 12i, while the velocity of the boat relative to the river is v2 = 5j where v1 and v2 are measure in m/s

(i) find the magnitude of the actual velocity of the boat.

(ii) find how long it takes the boat to cross the river and the distance it has traveled downstream in doing so

Homework Equations





The Attempt at a Solution


(i)(12^2 + 5^2)^(1/2) = 13 m/s

(ii) relative distance/relative speed = 240/5 =48 s

48(12) =576 m

can somebody tell if part (ii) is right the back of my book seems to use 12 as the relative speed since it says it takes 20 seconds.
Any help would be appreciated.
 
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Your solution is correct.

ehild
 
yes, it looks as if the book has got the 12 and the 5 the wrong way round :redface:
 
Thanks.
 
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