Work, Energy and Power — Prelims Strategy

Prelims Strategy

Identify the requested quantity and write its unit before substituting numbers. Work and energy are in joules, power is in watts, and kilowatt-hours measure energy. A unit check can expose a division where multiplication was needed, but it cannot by itself detect a wrong sign or an omitted angle.

For work, isolate the named force and its component along displacement. If the question asks for net work, include the other force contributions. For a kinetic-energy change, calculate the difference of squared speeds; do not square the speed difference. Keep any stated approximation for gravitational acceleration and avoid replacing it with an unstated value.

For a machine comparison, distinguish useful output from input and average from instantaneous power. Equal delivered energy with different times determines a rate comparison, not an efficiency comparison.

Read the scope of conservation carefully: mechanical energy can decrease while a wider total-energy account includes the transfer into internal forms. After solving, identify what each numerical distractor represents, such as final energy, initial energy, an unprojected force product or a missing conversion factor.