We have been given a set of questions to do. Most of these I have managed fairly easily but there are some which I am really stuck on and am getting quite annoyed with now as I have been working at them for ages! Help on any of these would be really appreciated: The Saturn V rocket which launched the Apollo space missions had the following specifications: mass at lift-off = 3.0 x 10^6 kg velocity of exhaust gases = 1.0 x 10^4 m/s initial rate of fuel consumption at lift-off = 3.0 x 10^3 kg/s 1.(a) Calculate: (i) the force (thrust) produced at lift-off (ii) the resultant force acting on the rocket at lift-off 2.(a) An empty railway truck of mass 10000kg is travelling horizontally at a speed of 0.5m/s. (had to calculated the momentum and kinetic energy - not sure if this will help with the bit im stuck with!) Sand falls vertically into the truck at a constant rate of 40kg/s. Calculate the additional horizonal force which must be applied to the truck if it is to maintain a steady speed of 0.5m/s. Thanks for anyones help - I can usually manage these kind of questions but I'm really stuck for some reason!!