Question

If I know the state of a system at two different times, but don't know how much time has passed between them, it makes more sense to use:

A The momentum principle

B Conservation of energy

Answer 1

The state of a system refers to the energy state or the energy level.

i) The change in momentum of a system is equal to the product of the force and time interval during which this force is acting upon the system. This is the momentum principle.

ii) Conservation of energy states that the work done by a conservative force on a system will be equal to the change in kinetic energy of the system. So here we are not worried about the time interval or the magnitude of force. We just need the energy states to calculate the work done and further evaluate the problem.

So if we the state of a system at two points of time but not the time period, it makes sense to use the conservation of energy principle.