Special relativity of a light source moving downstream

[matt_crouch]

Homework Statement

Let Cw be the speed of light through water at rest. Water is now flowing at speed v parallel to the x-axis according to one observer, and there is also a light source moving with the water at speed v

1) what is the speed at which the light source sends light signals in the downstream direction?
2) what is the speed at which the light source sends light signals in the upstream direction
3) What happens for the upstream light signal, if v<cw?

a. the signal propagates in the positive x direction
b.the signal propagates in the negative x direction
c the signal propagates at zero speed

Homework Equations

The Attempt at a Solution

i don't really know where to start. I was going to use the equation

x=(gamma)(x'-vt')
but since we don't have the time
im not really sure thanks in advance

 

[matt_crouch]

anyone?

 

[Doc Al]

Hint: How do velocities add relativistically?