Work & Power — Drills · Grade 12 Science
Chapter: Work, Energy & MomentumWhat these drills covers
By the end of Work & Power you should be able to:
- I can calculate the work done by a force using W = Fd (and W = Fd·cosθ when the force acts at an angle).
- I can apply the work-energy theorem and calculate power with P = W/t.
6 questions, numeric, multiple choice and written answer, each with a worked explanation.
Vocabulary used: work, joule (J), work-energy theorem, power, watt (W).
Problem 1
Answer and explanation
90 J
W = Fd = 15 × 6.0 = 90 J.
Problem 2
Answer and explanation
150 W
P = W/t = 300 ÷ 2.0 = 150 W.
Problem 3
Answer and explanation
980 J
The lifting force equals the weight mg = 20 × 9.8 = 196 N. W = Fd = 196 × 5.0 = 980 J.
Problem 4
- joule
- newton
- watt
- pascal
Answer and explanation
watt
Power is the rate of doing work, measured in watts (1 W = 1 J/s). The joule is the unit of work and energy.
Problem 5
Answer and explanation
Work is the energy transferred when a force acts through a displacement (W = Fd), measured in joules. Power is the rate at which work is done or energy is transferred (P = W/t), measured in watts. Two machines can do the same amount of work, but the one that does it in less time has greater power.
Problem 6
Answer and explanation
300000 W
P = Fv = 20,000 × 15 = 300,000 W (300 kW).