1) Calculate the force exerted on a rocket, given that the propelling gases are expelled at a rate of 1500 kg/s with a speed of 4.0 x 10^4 m/s (@ the moment of take off) Answer: 6.0 x 10^7 N Okay I can not figure how to get an equation to use... Though I did noticed that the rate x the speed in this problem does in fact give you 6.0 x 10^7. Does that play a role? --- 2) A 12,600 kg railroad car travels alone on a level frictionless track with a constant speed of 18 m/s. A 5350 kg load, intially at rest, is dropped on to the car. What will be the car's new speed? Answer: 12.6 m/s So... here was my approach... (Before) KE1 + KE2 ( = 0) = (after) KE1 + KE2 (1/2)(12600 kg)((18 m/s)^2) + 0 = (12600 +5350)(v^2) sq root of 114 = 10.6 m/s... I am off by 2 numbers... did I do something wrong? --- 3) An atomic nucleus intially moving @ 420 m/s emits an alpha particle in the direction of it's velocity, and the remaining nucleus slows to 350 m/s. If the alpha particle has a mass of 4.0 u and the original nucleus has a mass of 222 u what speed does the alpha particle have when it is emitted. Answer: 4.2 x 10^3 m/s I did the same approach as above with Kinetic energies... Cannot figure out what I am doing wrong. Please help me.