Physics
What this domain tests
Physics questions assess mechanics, energy and momentum, waves and optics, and electricity and magnetism, often through quantitative problems and diagram-based reasoning. Units and vector directions matter.
Mechanics
Newton's first law: no net force means no change in velocity. Second law: F_net = ma. Third law: forces occur in equal and opposite pairs on different objects. Use free-body diagrams to resolve forces into components. For constant acceleration, use kinematics equations; for circular motion, centripetal force points toward the center. Momentum is conserved when net external impulse is zero.
Energy and momentum
Work = Fd cos(theta). The work-energy theorem relates net work to change in kinetic energy. Mechanical energy is conserved when only conservative forces act. In collisions, momentum is conserved; kinetic energy is conserved only in elastic collisions.
Waves, optics, and electricity
Wave speed v = f(lambda); frequency is set by the source. Snell's law: n1 sin(theta1) = n2 sin(theta2). Ohm's law: V = IR. In series, current is the same and resistances add; in parallel, voltage is the same and reciprocal resistances add. Power P = IV = I2R = V2/R.
Worked example
A 2.0 kg cart moving at 3.0 m/s collides with a stationary 4.0 kg cart and they stick together. Find final velocity and kinetic energy lost. Momentum before = (2.0)(3.0) + 0 = 6.0 kg m/s. After, total mass = 6.0 kg, so v = 6.0/6.0 = 1.0 m/s. Initial KE = 1/2(2.0)(3.0)2 = 9.0 J. Final KE = 1/2(6.0)(1.0)2 = 3.0 J. Loss = 6.0 J.
Traps
Keep direction signs for velocity and momentum. Do not use conservation of kinetic energy in an inelastic collision. Do not mix series and parallel rules. Check whether a force does work when it is perpendicular to motion.