Question

Topic IVB: Momentum carried by an electromagnetic wave You are on a spacewalk on the International Space Station. You get separated from the station, and try to use your space suit's rockets to push you back. Unfortunately, they run out of fuel. Now you are a distance of 23.5 m from the station, with zero speed relative to the station. You are carrying a 210 W flashlight. You decide to turn on the flashlight and use it as a "light rocket" to propel you back to the station. If the flashlight has a mass of 4.7 kg, and you and your space suit have a combined mass of 115 kg, how long will it take you to get back to the station? Note that we've derived an equation for radiation pressure in terms of intensity, and that what we need is an equation for force in terms of power. Remind yourself how force is related to pressure and how intensity is related to power - you can then take the pressure vs. intensity equation and change it into a force vs. power equation. Note: you can enter hours as a unit in LON-CAPA with the symbol "hr." 24.9 hr Opts You are correct. Your receipt no. is 154-2212 Even though you have had your flashlight for many spacewalks, you decide that you do not want to wait all that time to get back to the station. So instead you plan to throw your flashlight. If the maximum speed that you can throw the flashlight with your spacesuit on is 5 m/s, how long would it take you to get back to the station?

Answer 1

1] Intensity is related to radiation pressure by:

I = pc

and Intensity = Power/Area; Pressure = Force/Area

=> P/A = (F/A)c

=> P = Fc

acceleration is then: a = P/([m+M]c)

using S = ut + (1/2)at², determine t. This gives, t = 24.902 hours.

2] Use conservation of linear momentum.

(M+m)(0) = Mv + m( - 5)

0 = 115v + 4.7( - 5)

=> v = 0.204 m/s

this will be your speed after throwing the flashlight. With this speed, the time taken to reach the station will be:

t = distance / speed = 23.5/0.204 = 115 seconds = 1 minute 55 seconds.

This is how long it would take for you to get back to the station.