NUST NET Physics · Physics · Mechanics. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Work is done when a force moves its point of application. Only the part of the force along the motion counts, so a force at right angles to the motion does no work. If the force changes with distance, the work is the area under the force-displacement graph.
Work done on a body changes its energy. The net work equals the change in kinetic energy. When there is no friction, kinetic plus potential energy stays constant, which often gives the answer faster than the equations of motion. With friction, the work done against it is the mechanical energy lost.
Power is the rate of doing work.
Treating kinetic energy as proportional to speed. It depends on v2, so doubling the speed makes the kinetic energy (and the braking distance) four times as large.
Answer: 10 m s−1
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