1. The problem statement, all variables and given/known data A 1600 kg object is initially at rest 400 km above the earth’s surface. The object falls straight down and generates 8.3x10^8J of heat energy while descending to an altitude of 100 km. What is the velocity of the object at this altitude? (http://i1070.photobucket.com/albums/u488/ScatlettArmadillo/Question20.jpg) 2. Relevant equations Ek = (mv^2)/2 Ep = -GMm/r G=6.67^-11 Mass of Earth = 5.98x10^24 kg Radius of Earth = 6380000 m Force of Gravity = GMm/r^2 3. The attempt at a solution http://i1070.photobucket.com/albums/u488/ScatlettArmadillo/Question20-1.jpg Once I got to the final step I had to find the root of a negative, which is not possible, so I must have made an error somewhere else, but I can't seem to work out where.