Hi guys. I'm new to this forum so I'm not sure if I'm posting this in the right place or correctly, but I was totally stumped on a Physics 12 question as I was studying for my exam. The question is: An explorer spacecraft is descending towards Mars using a rocket engine for braking. The spacecraft has Ep = -2.8x10^10 J and Ek = 3.0x10^9 J at its initial position. Some time later the spacecraft has Ep = -3.4x10^10 J and Ek =1.0x10^9 J. How much work did the rocket engine do in braking the spacecraft? At first, I thought it was work done = change in kinetic energy, but that's not the answer. Then I realised that the change in kinetic energy and the change in potential energy were not the same, and that's where I was completely lost. What does it mean when its gravitational potential energy increases in the negative? Is it moving closer or farther from the planet? And how would I go about solving this question? I tried (although I don't know why): Wbrakes - [(-3.4x10^10) - (-2.8x10^10)] = -2.0x10^9; Wbrakes = -2.0x10^9 - 6.0x10^9 = -8.0x10^9 J which is the correct answer. I just don't know if that's the correct solution and if it is, why.