The watt, W; one joule per second.

State the work-energy principle.

The total work done on a body equals its change in kinetic energy.

At maximum speed on a level road, what is F?

F=R: the driving force equals the resistance.

How should a speed change be used in kinetic energy?

\frac12m(v^2-u^2), not \frac12m(v-u)^2.

Power in kW: what must you do first?

Convert to watts: multiply by 1000.

Work, energy and powerEdexcel International A Level Further Maths: Flashcards

Card 1 of 120 of 12 known

Question

Kinetic energy formula?

Tap or press Space to reveal

Tap card or press Space to flip

See all 12 cards

Kinetic energy formula?: $\frac12mv^2$
Gravitational potential energy formula?: $mgh$
Work done by a constant force at angle $\theta$ to the motion?: $Fd\cos\theta$
Power in terms of force and speed?: $P=Fv$
Unit of power?: The watt, W; one joule per second.
State the work-energy principle.: The total work done on a body equals its change in kinetic energy.
Work done against gravity moving $d$ up a slope at $\alpha$ ?: $mgd\sin\alpha$
Friction on a rough slope?: $F=\mu R$ with $R=mg\cos\alpha$ .
At maximum speed on a level road, what is $F$ ?: $F=R$ : the driving force equals the resistance.
Driving force for a car at constant speed up a slope?: $F=R+mg\sin\alpha$
How should a speed change be used in kinetic energy?: $\frac12m(v^2-u^2)$ , not $\frac12m(v-u)^2$ .
Power in kW: what must you do first?: Convert to watts: multiply by $1000$ .

Exam questions on Work, energy and power

A car of mass $1200$ kg moves along a straight horizontal road. The engine works at a constant power of $24$ kW and the resistance to motion is a constant $800$ N.
Find the increase in the car's kinetic energy as its speed increases from $15$ m s $^{-1}$ to $30$ m s $^{-1}$ .2 marks
A box of mass $5$ kg is pulled from rest up a line of greatest slope of a rough plane inclined at $20^\circ$ to the horizontal, by a constant force of $40$ N acting parallel to the plane. A constant frictional force of $8$ N opposes the motion. Take $g=9.8$ m s $^{-2}$ . The box moves $6$ m up the plane.
Find the speed of the box after it has moved $6$ m.2 marks
A lorry of mass $6000$ kg moves up a straight road inclined at an angle $\alpha$ to the horizontal, where $\sin\alpha=\frac{1}{20}$ . The resistance to motion is a constant $1500$ N. Take $g=9.8$ m s $^{-2}$ .
The lorry travels up the road at a constant speed of $12$ m s $^{-1}$ . Find the power of the engine.3 marks

See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).