# Change in momentum: problem

1. Jan 6, 2007

### Methavix

hi all,
i have this problem to solve.

there are 2 parallel plates in the vacuum, the first one (the secondary plate, for example on the left) is mechanically connected to the second one (the metal plate, on the right) with a little very hot cylinder in the center (it heats the second plate because are attached each other and emits photons in any direction for the black-body law). the second plate is very hot too (thank to the cylinder) and emits photons (black-body radiation) from both of its faces. i want to know the final thrust (o final momentum) of the structure (the component parallel to the central axes), considering all faces perfectly reflecting.

besides, if the left face of the second plate (that is the face in front of the first plate) is covered by a material perfectly absorbing what does it happen? what is the thrust or momentum? the second plate in that side doesn't emits photons? or it emits photons but when come back from the first plate it absorbs them?

at this address there is a simple scheme of the structure http://www.associazionemicene.it/reactor.jpg

thanks
--
Luca