Momentum

A science passage about collisions is really asking one question: does momentum add up the same way before and after? Momentum is p = mv, mass times velocity. In any collision where no outside push or drag acts on the system, total momentum before equals total momentum after. That is the whole rule. It holds whether the objects bounce apart, stick together, or crumple. You read a table or graph, add up mass times velocity for everything going in, and set it equal to the same sum going out.

Kinetic energy is a different story. KE = (1/2)mv² is not automatically conserved, because collisions can turn motion into heat, sound, and deformation. A collision that keeps all the kinetic energy is called elastic; one that loses some is inelastic. When two objects stick together, that is the most inelastic case possible, and it always loses the most kinetic energy while momentum still balances. A passage showing momentum staying flat but kinetic energy dropping is just describing an ordinary inelastic collision, not a broken rule.

This sits next to force and energy items because momentum connects them: force equals mass times acceleration, and a collision applies a brief force that changes velocity, hence momentum, over a short time. Expect a data table or a before-and-after diagram with masses and velocities, and a question asking you to conserve one quantity (momentum) while energy visibly changes. The truck-versus-bicycle style question is testing whether you remember that mass counts just as much as speed.