Question

Which of these follows from Newton's laws about the energy of a moving object?

The kinetic energy of an object remains the same if friction is absent.

The total mechanical energy of an object is always constant.

The mechanical energy remains the same if there are only conservative forces acting.

The total of all forms of energy is always constant.

Answer 1

I think the first statement, THE KINETIC ENERGY OF AN OBJECT REMAINS THE SAME IF FRICTION IS ABSENT, follows from Newton's laws about the energy of a moving object. It is related to Newton's 1st law of motion.

Newton's 3 laws of motion.

First law:In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a net force.

Second law:In an inertial reference frame, the sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma.

Third law:When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.