# Need help with an exam review question

1. Jan 16, 2005

### Lisa... needs help

Hey, i'm practising some exam review questions that i was given but i can't figure this one out

A sunbather, drifting downstream on a raft, dives off the raft just as it passes under a briidge and swims against the current for 15 mins. She then turns and swims downstream, making the same total effort and over taking the raft when it is 1.0km downstream from the bridge. What is the speed of the current in the river?

If someone could help me that would be great!

2. Jan 16, 2005

### dextercioby

We're not gonna do the problem for you.We'll only help,if you get stuck.By the looks of it,you haven't even started...
Post you work...

Daniel.

3. Jan 17, 2005

### Lisa... needs help

opps sorry - i have tried it - many times!?
okay... i tried making up different formulas and substituting them into each other such as:
d1=(Vs-Vc)(900s)
d2=(Vs+Vc)t
d1=d2 (for the time before she gets back to the bridge)
900Vs-900Vc=Vst+Vct
and then i didn't know where to go from there?

i also tried:
d1=(Vs-Vc)(900s) -> Vs=(d/900)+Vc
d2=(Vs+Vc)t -> Vs=(d/t)-Vc

Vs=Vs
and got it down to
(d1/900)+2Vc=(d2/t)

I've tried many other similar ways, but i'm not really sure if i'm heading in the right direction, messing up on the math or what?

4. Jan 17, 2005

### dextercioby

No,you're not messing up the math,it's just that,the way i see it,it's too little data.I get 3 equations with 4 unknowns.And i can't solve them...

Maybe i'm missing something,but i double checked and still another equation is absent...

Daniel.