# Maths

A river flows at 0.3 ms. Peter and Mary, who can each swim at 0.5 ms' in still water, wish to cross the river. The river is 20 metres wide.Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b 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.
ili How long does it take her to reach the other side?
i've been stuck on this question too!
someone pls respond
desperate times
Original post by darkandsky12
i've been stuck on this question too!
someone pls respond
desperate times

oh my god
and i thought it was jsut me
stupid g and t
Original post by sorrymenotyou
A river flows at 0.3 ms. Peter and Mary, who can each swim at 0.5 ms' in still water, wish to cross the river. The river is 20 metres wide.Peter aims straight across the river, and is carried downstream by the current.
i How long does he take to reach the other side?
il Work out his actual speed of travel. b 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.
ili How long does it take her to reach the other side?

Original post by darkandsky12
i've been stuck on this question too!
someone pls respond
desperate times

what have you tried so far?

Spoiler

well i basically dont understand why part a i and a ii are not the same as part b ii and part b iii? Is it not asking the same thing twice?
also im confused on what to do with perpendicular vectors- do i just rearrange them to make them tip to tail? Thanks!
Original post by sorrymenotyou
also im confused on what to do with perpendicular vectors- do i just rearrange them to make them tip to tail? Thanks!

pretty much (I think so anyway, been a while!)

Original post by sorrymenotyou
well i basically dont understand why part a i and a ii are not the same as part b ii and part b iii? Is it not asking the same thing twice?

no, the people end up at different points on the other side of the river.
Original post by bl0bf1sh
pretty much (I think so anyway, been a while!)

no, the people end up at different points on the other side of the river.

oh ok right so is mary affected by the 0.3ms current too?
Mary need her resultant vector to be perpendicular to the bank.
Original post by sorrymenotyou
oh ok right so is mary affected by the 0.3ms current too?

yes! if you imagine swimming across a river, you'll have to adjust your swimming due to the flow of the river, otherwise you'll end up who knows where downstream

can you try drawing some diagrams?