Law of conservation of physical and mechanical energy In the following motions, the mechanical energy conserved is () 1. An object moving at a constant speed on a smooth horizontal plane 2. An object moving in a circular motion at a uniform speed 3. An object that slides along a smooth slope 4. Throwing a moving object horizontally (please write down why it is right and why it is wrong)

Law of conservation of physical and mechanical energy In the following motions, the mechanical energy conserved is () 1. An object moving at a constant speed on a smooth horizontal plane 2. An object moving in a circular motion at a uniform speed 3. An object that slides along a smooth slope 4. Throwing a moving object horizontally (please write down why it is right and why it is wrong)

1 3 4
1. When sliding on a smooth plane, there is no friction. The consumed velocity never changes. The gravitational potential energy does not change, that is, the initial velocity of 0.5mv ^ 2 = 0.5mv, and the final velocity does not change, so it is conserved
2. In the vertical plane, the resultant force is not necessarily changing
3. Smoothness means that there is no friction. It means that the initial velocity is 0 and the gravitational potential energy is directly converted into kinetic energy
4. The ideal horizontal projectile (it seems that the horizontal projectile is idealized) has no resistance, but has an initial velocity, and the final velocity is greater than the initial velocity, because the gravitational potential energy becomes kinetic energy