Physics
What this section tests
Physics items emphasize motion, forces, energy, waves, electricity, and density and pressure - mostly single-formula applications with careful unit tracking.
Formulas to know
- Speed = distance ÷ time; velocity adds direction (a vector).
- Acceleration = change in velocity ÷ time.
- Newton’s second law: force = mass × acceleration.
- Weight = mass × gravity (about 9.8 m/s² on Earth); weight is a force in newtons, mass is in kilograms.
- Work = force × distance; power = work ÷ time (watts).
- Kinetic energy = ½mv²; potential energy = mgh.
- Wave speed = frequency × wavelength.
- Ohm’s law: voltage = current × resistance.
- Density = mass ÷ volume.
Traps to expect
- Mass vs. weight. Mass stays the same on the Moon; weight changes.
- Net force zero means constant velocity - the object is not necessarily at rest.
- Units mismatched (minutes with hours, grams with kilograms) before substituting.
- Confusing work with power: work is the total, power is the rate.
- Scalar vs. vector: speed has no direction, velocity does.
Rule of thumb
Write the formula, convert every quantity to standard units (meters, seconds, kilograms, newtons, joules, watts), substitute, then check the unit of the result against what the question asks for.
Worked example
A 60 kg student climbs a 3 m staircase in 4 s. What power is produced? Work = mgh = 60 × 9.8 × 3 = 1,764 J. Power = 1,764 ÷ 4 = 441 W (about 440 W). Note that mass was converted only if given in grams, and time was already in seconds.