MECEE-BL Physics: laws applied to short numerical situations
What the physics paper tests
Mechanics, heat, waves and sound, electricity and magnetism, optics and modern physics. The paper favors applying a law to a short situation: a block on an incline, a lens, a resistor network or a photoelectric cell. Keep a symbol list and a unit check for every numerical answer.
Core rules
- Newton's second law: F_net = ma; resolve forces along and perpendicular to motion.
- Kinematics: v = u + at, s = ut + ½at², v² = u² + 2as, valid for constant acceleration.
- Work-energy: work done by net force equals change in kinetic energy.
- Ohm's law: V = IR; series resistances add, parallel conductances add.
- Lens/mirror formula: 1/f = 1/v − 1/u (lens) with sign convention; power P = 1/f in metres.
- Photoelectric effect: eV_s = hf − φ; below threshold frequency no emission occurs.
Worked example
A 2.0 kg block on a frictionless horizontal surface is pulled by a constant 10 N force from rest for 3.0 s. Acceleration a = F/m = 10/2.0 = 5.0 m/s². Final velocity v = u + at = 0 + 5.0 × 3.0 = 15 m/s. Distance s = ut + ½at² = 0 + ½ × 5.0 × 9.0 = 22.5 m. Check: work done = 10 × 22.5 = 225 J, and ΔKE = ½ × 2.0 × 15² = 225 J.
Traps
Keep signs consistent in projectile and lens problems. Convert cm to m before using P = 1/f. Do not add series and parallel resistors by the same rule. In waves, frequency is set by the source; speed changes with medium. In modern physics, use frequency, not intensity, to decide whether emission occurs.