- #1
Sparky_
- 227
- 5
Homework Statement
a student want to cross a river flowing east at a rate of 2.0km/hr in a boat on the south bank and arrive at point L on the north (north and west) side. Point L is 0.5km to the left or west from the starting point (point K - point K is on the south side). Point L is 0.5km (to the left) from a perpindicular line drawn from the starting point (K)
The student can row at 5.0km/hr.
How long will it take to paddle north-west up stream and arrive at point L?
Homework Equations
the picture
L ----------0.5km ------------M
.......|
.......|
.......0.25km -> flow = 2km / hr
.......|
.......|
(K)
The Attempt at a Solution
It has been a very long time since I have worked these types of problems and just for fun I tried my hand at this - no luck
I said the student can row at 5km/hr north and (5-2) km/hr westward
He will need to paddle the length of the hypotenuse or SQRT((0.25)^2 + (0.5)^2) = 0.559 km
The students velocity vector is SQRT((5)^2 + (3)^2) = 5.83 km/hr.
I see this is wrong - his velocity is faster than he can paddle.
My direction was to acquire his velocity vector and divide the hypotenuse distance (0.5590km) by the new velocity vector.
I know this is wrong - I have the answer - 0.17858 hr.
Am I wrong to think in terms of a velocity vector?
Is this to be solved with simple position equations?
Help??
Thanks
Sparky_