Hello everyone, the problem I have to solve is as following. You're in space and you're moving with a constant speed. Now, you want to accelerate. For this you will be using Newton's third law. Xenon 1+ iones will be shot from the back of the spacecraft with high speeds, the avarage speed an ion will be accelerated to is 30.000 m/s. This will result in a gain in velocity of the spacecraft, according to Newton's 3rd law. Calculate how many velocity a spacecraft with a mass of 1000 kg can gain by shooting away 50kg of Xenon 1+ iones. My attempt: Mass of one Xenon +1 ion: = 131.30 x 1.660538921 x 10^-27 = 2.18 x 10^-25 kg Kinetic energy gain of ion: 1/2 mv^2 = 1/2* 2.18*10^-25 *30000^2 = 9.81*10^-17 Joule According to newton's third law the gain in kinetic energy of the ion should be equal to the gain in kinetic energy of the spacecraft, right? (not sure about this) 1/2 mv^2 = 1/2 * 1000 * v^2 = 9.81*10^-17 v = 4.43 * 10^-10 m/s for every ion shot Calculating how many iones we have: 100000 / 131.30u = 761.614 mol. 761.614 * 6,022 * 10^23 = 4.586 * 10^26 iones. Shooting away all those iones will create a gain in speed of: 4.586 * 10^26 * 4.43 * 10^-10 = 2.03 * 10^17 m/s But since this is about a few thousand times the speed of light, I assume I did something wrong somewhere. If anyone could help me I'd be very thankful. Sander.