# Kinematics problem

1. Oct 29, 2006

### ellusion

A swimmer who can swim at a speed of 0.8 m/s in still water heads directly across a river 86m wide. the swimmer lands at a position on the far bank 54m downstream from the starting point. determine:

a) the speed of the current
b) velocity of swimmer relative to the shore
c) the direction of departure that would have taken the swimmer directly across river

so far i drew myself a picture and found the distance he covered and the time it took him. from there im just stuck, how do i find the speed of the current.

2. Oct 29, 2006

### geoffjb

How far down the stream (a component of his total distance--be careful) did the current move him (displacement) and how long did it take to displace him that distance?

3. Oct 29, 2006

### ellusion

the current moved him 54m down the stream hwo would i get the time

what do you mean by a component of his total distance?

Last edited: Oct 29, 2006
4. Oct 29, 2006

### ellusion

if he were to swim across and there is no current his time would be 107.5s
so could i just plug that to find the velocity of the current
v=d/t
= 54/107.5
=0.50m/s

can i do that

5. Oct 30, 2006

### OlderDan

Yes. Since the swimmer is heading directly across the river, his crossing time is unaffected by the current. If he swam so that he moved directly across the river, his heading would be upstream and that would change his crossing time.