# Electromagnetic problem

1. Apr 10, 2007

### yogi41

I've been trying to do this problem for about 2 hours now. I can't seem to find the right equations to use. Any help would be appreciated

A spacewalking astronaut servicing an orbiting space telescope has run out of fuel for her jet pack and is floating 20.0 m from the space shuttle with zero velocity relative to the shuttle. The astronaut and all her gear have a total mass of 150kg. If she uses her 220w flashlight as a "light rocket," how long will it take her to reach the shuttle?

2. Apr 10, 2007

### jsbhk

the light that a 220w flashlight generates does not create thrust, but the heat it produces will give you a thrust! She will arrive at the shuttle eventually if she doesn't run out of oxygen.

We can look at Newton's Law F=m x a

We don't know the Force produced by the flashlight, otherwise we can calculate it very easily:

Force = mass x acceleration

Force produced by the flashlight = 150kg x 20m/time/time

3. Apr 10, 2007

### jsbhk

I forgot watt is energy in newton per hour? If so, 220w is 220N/hour, LOL, wild guess, shoot me if got it wrong.

220N per hour = 150 x 20/time square

220N per hour = 3000 / time square

sqaure root 220N per hour = 3000 / time

14.832 per hour = 3000 / time

3000 / 14.832 per hour = time

202.265 hours = time

202 hours !!! She is dead, trust me, LOL.............

Last edited: Apr 10, 2007
4. Apr 10, 2007

### yogi41

i know watt is joules per second. In the back of my book the answer is 25.1 hours. But i still can't seem to get anywhere close to that answer. I even tried E=c*p

5. Apr 10, 2007

### jsbhk

Hey, I just checked my text book, 1W=1 newton meter per second!

220W = 220 Newton Meter Per Second!!!

6. Apr 10, 2007

### jsbhk

220Newton Meter per hour = 150Kg x 20M/time/time

220N Meter per hour = 3000/time /time

220N = 3000/time/time / Meter per hour

220 = 3000 /time (in hour)

3000 / 220 = time (in hour)