A cart of mass m is moving with negligible friction along a track with known speed y, to the right. It collides with and sticks to a cart of mass 4m moving with known speed y, to the right. Which of the two
principles, conservation of momentum and conservation of mechanical energy, must be applied to determine
the final speed of the carts, and why?

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force