Force Created by a Laser (EM)

1. Oct 23, 2012

bmb2009

1. The problem statement, all variables and given/known data
Two astronauts are at rest in outer space, one 15.3 m from the Space Shuttle and the other 30.6 m from the Shuttle. Using a 123.0-W laser, the astronaut located 30.6 m away from the Shuttle decides to propel the other astronaut toward the Space Shuttle. He focuses the laser on a piece of totally reflecting fabric on her space suit. If her total mass with equipment is 129.0 kg, how long will it take her to reach the Space Shuttle?

2. Relevant equations

Force=Power/c

3. The attempt at a solution

Since Force=Power/speed of light

F=(123W)/(3x10^8)
F=4.1E-7 since F=ma (4.1E-7)/129kg = accel= 3.178E-9 m/s^2

the laser causes constant acceleration so...
Df=Do + VoT+ 1/2aT^2
and I solved for T... with Df = 15.3 meters, Do and Vo both equal 0.

but this didn't work and I have no idea where to go from here. Does the distance of the second astronaut (the one shooting the laser) affect the calculation? Any help?
Thanks!

2. Oct 23, 2012

Vodkacannon

This is just a suggestion:
If it's a totaly reflecting surface shouldnt the force (F) of the beam be doubled?

Just like if water hits the back of a spoon as compared to the front of a spoon. The water hitting the front is deflected and therefore puts a greater force on the spoon.

3. Oct 23, 2012

bmb2009

I just tried your hunch and you were correct. Thanks a bunch!