1. The problem statement, all variables and given/known data In each of the following, an order of magnitude estimate is required. Estimate i) the gravitational energy of a 100kg satellite in low earth orbit, the velocity of the satellite, and the period of the orbit. ii) the kinetic energy of a car travelling at 70mph and the power output of a car engine. 2. Relevant equations 3. The attempt at a solution Solution: i) U = GMm/r2, where r = radius of (low earth) orbit radius of earth = 6400 km and mass of earth = 6*1024 kg. Plugging numbers gives U = 6.3*109 J. Such a big number looks a bit odd. Is this a realistic number? (or am I worng somewhere?) v = sqrt(GM/r), so v = 750 km/s. Assuming a circular orbit, v = 2*pi*r/T, so the time period T = 52s. !!!!!!!!! I think this means my velocity is wrong, which U is wrong, but where IS the mistake? ii) 1 mile = 1.6 km. mass of (typical) train = 2000 kg. So, K = 0.5mv2 = 3.1*104 J. I don't know how to work out the power. Any help I would greatly appreciate.