astronomy
posted by james .
Calculate the average speed of a water molecule (with a mass of 3.0e26 kg) on the hot side of Mercury (710 Kelvin).

This is definitely not my area but try some of the following sites to see if anything will shed light on your problem:
http://search.yahoo.com/search?fr=mcafee&p=Calculate+the+average+speed+of+a+water+molecule+%28with+a+mass+of+3.0e26+kg%29+on+the+hot+side+of+Mercury+%28710+Kelvin%29.+
Sra 
model the water molecule as having kinetic energy, or the speed= sqrt (3/2 RT/m)
this is the rms speed, not average.