1. A 160.0Kg cannon initially at rest shoots an 8.00Kg cannon ball at a speed of 240.0 m/s. The cannon moves backwards 0.40 meters. What is the force on the cannon after firing the cannon ball? I've solved for the velocity of the cannon, getting 12 m/s, but don't know exactly where to go from there. 2. An 80kg astronaut is in space, at rest. He throws a 5kg tool at 6.0 m/s to another astronaut, with a mass of 65 kg, who catches it. c. How much energy is used by the astronaut throwing the tool Is it wrong to use 1/2(m)(v)^2? I used that to get an answer of 90 J, but I've been told the answer was 96 J. Any help is appreciated, I know this is probably very basic to some of you.