A rocket at rest on the ground with initial mass 20,000 kg, 80% of which is fuel, burns 200kg/s as it flies directly upwards. The exhaust gas exits the rocket at a relative speed of 1.80 km/s. Find (a) the thrust of the rocket, (b) how long it takes to exhaust its fuel, and (c) the rocket's speed at the end of its engine burn. Assume g is constant and neglect air resistance