[SOLVED] force in a non-isolated system I don't normally do something like this, but I'm stuck on my homework. A lizard jumps, pushing with its legs against the ground. Assume the lizard's inertia is .05 Kg. Its center of mass starts out .5 cm above the floor, and raises 1 cm to 1.5 cm while it is pushing against the floor. At that height, its feet lose contact with the floor and it continues to travel up to a height of .15 m. What is the magnitude of the average force exerted by the floor on the lizard? I know that F=ma, but I have no idea how to find the acceleration without the time the action took. I also know that if I have to use the change in center of mass, I'll have to convert the cm to m. But other than that, I'm totally lost. Any help would be appreciated.