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# help with mechanics/vectors? watch

1. done
2. Hi! I've moved this into the Maths forum for you - hopefully someone will be able to help you out here
3. (Original post by an1megod)
A river flows at 0.3m/s. Peter and Mary, who can each swim at 0.5m/s in still water, wish to cross the river. The River is 20 metres wide.

a) Peter aims straight across the river, and is carried downstream by the current.
i) how long does he take to reach the other side?
ii) work out his actual speed of travel

Mary swims to the closest point on the opposite bank.
i) in which direction does she aim?
ii) work out her actual speed of travel
iii) how long does it take her to reach the other side?

I don't understand what I have to do with this question at all. Just need some pointers.
in both cases you need a rightangled triangle of vectors...

for Peter the two short sides will be his still water speed and the current speed

for Mary the long side will be her still water speed and one of the short sides will be the current speed.

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Updated: February 15, 2018
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