Grade 12 Physical Sciences · Mechanics

Calculate mechanical power

Calculate how fast work is done using P = W/Δt or P = Fv (a motor doing 600 J in 2 s has a power of 300 W).

past paper questions use it: 4 past paper questions use it
videos: 3 videos

Learn it: calculate mechanical power

Pick one and watch it, then try the questions below. Videos load only when you tap play.

Grade 12 work energy and power : Power calculationKevinmathscience

Power Calculations Part 1: Work Energy Power Grade 12 PhysicsMiss Martins Maths and Science

Power of an electric motor: Power part 3: WEP grade 12 PhysicsMiss Martins Maths and Science

Now try it on a real exam question

No sign-up. Takes 3 minutes.

Question 1.5 · May/June 2025 · Paper 1 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.

1.5 Engine P has a greater maximum power output than engine Q.

Which ONE of the following statements is CORRECT when P and Q each operate at their maximum power output?(2)

A Q does more work than P in the same amount of time.
B P and Q do the same amount of work in the same amount of time.
C P and Q do the same amount of work, but Q does it in a shorter time than P.
D P and Q do the same amount of work, but P does it in a shorter time than Q.

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

More past paper questions: calculate mechanical power

Work each one out first, then open the memo and check every tick.

3. Question 5.3.3 · May/June 2025 · Paper 1 · National (DBE) · 3 marks
Water is drawn from a water source $12, 5$ m below the ground by an electric pump. The water is lifted vertically upwards at a constant speed, as shown in the simplified diagram below.

The pump lifts the water upwards at a rate of $2, 5$ kg·s $^{- 1}$ . Ignore ALL frictional and capillarity effects.
5.3 The pump lifts $200$ kg of water from the source to the ground at a constant speed. Calculate the:
5.3.3 Average power dissipated by the pump

Ignore energy losses in the form of heat and sound.(3)
Show the memo (3 ticks)Memo
1. ✓
  Formula $P = \frac{W}{Δ t}$
  1 mark · Calculate mechanical power
2. ✓
  Substitution $= \frac{24 500}{80}$
  1 mark · Calculate mechanical power
3. ✓
  Answer $= 306, 25$ W
  1 mark · Calculate mechanical power
4. Question 1.4 · November 2022 · Paper 1 · National (DBE) · 2 marks
Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.
1.4 A car travels at CONSTANT VELOCITY along a horizontal road. A constant frictional force acts on the car during its motion.

Which ONE of the following statements about the power dissipated by the engine of the car during the motion is CORRECT?

The power ...(2)
1. A is zero.
2. B increases.
3. C decreases.
4. D remains constant.
Show the memo (1 tick)Memo
1. ✓
  Power at constant velocityConstant velocity means $F_{n e t} = 0$ , so the engine's force equals the constant frictional force.
  $P_{a v e} = F v_{a v e}$ : both $F$ and $v$ are constant, so the power remains constant.
  
  Answer: D
  2 marks · Calculate mechanical power

Free on Android

Know exactly which skill is costing you marks.

Mark past papers tick by tick in the NavyBlue app. It remembers every mark you lose, shows you the skills to fix first, and picks your next questions.

The NavyBlue app showing a learner's weak skills