The density of a earth is given by p=3g/4πRG, where R is radius of earth G is gravitational constant. check the dimensional consistency of this relation

Imagine that someone pushes one marble toward a motionless marble. would there still be action-reaction forces involved in the collision? how might the marbles’ motions be changed? ?

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?

Using the free-body diagram, calculate the net force acting on the sled. is the sled in a state of dynamic equilibrium?