Physics 30 Diploma cheat sheet

Physics 30 - Momentum, Energy, and Fields Reference

• Momentum p = mv is a vector; total momentum of an isolated system is conserved in all collisions (p_before = p_after, summed as vectors).

• Impulse J = FΔt = Δp; the area under a force–time graph equals impulse, and a net external impulse is the only thing that changes total momentum.

• Elastic collision: kinetic energy and momentum both conserved. Inelastic: momentum conserved, kinetic energy not; perfectly inelastic means the objects stick together with common final velocity.

• For a perfectly inelastic collision of masses m1 (velocity v1) and m2 (velocity v2): v_f = (m1v1 + m2v2)/(m1 + m2).

• In a 1-D elastic collision the relative speed of approach equals the relative speed of separation: v1 − v2 = −(v1' − v2').

• Work–energy theorem: W_net = ΔKE = ½mv_f² − ½mv_i²; work W = Fd cosθ, with θ the angle between force and displacement.

• Gravitational potential energy near Earth's surface: ΔPE = mgΔh; conservation of mechanical energy applies when only conservative forces do work.

• Coulomb's law: F = kq1q2/r² with k = 8.99 × 10⁹ N·m²/C²; force is repulsive for like charges, attractive for opposite, and acts along the line joining them.

• Electric field E = F/q (vector, points in the direction of force on a positive test charge); for a point charge E = kq/r², and field lines point away from positive and toward negative charges.