Suppose I have a system of a person holding a rock on a frictionless sheet of ice. He throws the rock at an angle above the horizontal to propel himself off the ice. Is the momentum of that system truly conserved?
If it will help you understand me, I'll post the assignment verbatim:
You are standing on a large, thick sheet of frictionless ice and holding a large rock. In order to get off the ice, you throw the rock so it has velocity 12.0 m/s relative to the earth at an angle of 35.0 degrees above the horizontal. Your mass is 70.0 kg and the rock's mass is 6.00 kg.
- Assume first the entire momentum of the person-rock system is conserved. What will be your speed and in what direction will you move? Is this a desirable outcome of your attempt to get off the ice?
For the rest of the problem assume the ice does not break.- Is truly the entire momentum conserved in this case? If not, which part of the momentum is not conserved? What is necessary to cause a change in momentum and what is the cause in this case?
- What will be your speed after you throw the rock?
- What is the kinetic energy of the system before and after you throw the rock? Is kinetic energy conserved? If not, where does the additional energy come from?