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Standard Grade Physics

Name: ________________________ Class: _____ Teacher: __________________

"Measuring Energy"

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Section 3: MOVEMENT MEANS ENERGY

��Energy Transformations (Changes)For a Moving Vehicle

As a vehicle moves from one place to another, differentenergy transformations (changes) take place.

1) Complete the table to show the energy transformations(changes) taking place for each type of vehicle motion:

Type ofVehicle Motion

EnergyTransformation(s)

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��Work Done = Energy TransferredWhen a force moves an object through a distance,

the force does work on the object:

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The work done by the force on the object leads to atransfer of energy.

One form of energy is transformed (changed) toother forms of energy.

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2) Calculate thework done by

Matthew when hepulls a barrow full of

sand with aconstant force of 2 000 newtons

over a distance of 15 metres.

3) Charlene pushesher baby cousin'spram 50 metres

along the road byapplying a constant

force of 200 newtons.Calculate the work done.

4) In order to pulla sledge

75 metres acrossthe snow, a dogmust exert a constant force of

1 000 newtons. How much workmust the dog do?

5) Calculate theenergy transferred byTony when he pusheshis luggage 30 metres

with a constant force of230 newtons.

6) Calculate theenergy transferred by

Lee when he pulls arickshaw 200 metreswith a constant force

of 1 200 newtons.

7) How much energy istransferred by Michael

when he pushes hiscar 15 metres with a

constant force of1 500 newtons.

8) A horse does75 000 joules ofwork by pulling a

cart 25 metres witha constant force. Calculate the sizeof the force applied by the horse.

9) When Rianne pushesa wheelbarrow

12 metres with aconstant force, she does

13 800 joules of work.Calculate the size of the force

applied by Rianne.

10) A car pulls atrailer 500 metres

along the road witha constant force. The car transfers

1 800 000 joules of energy.Calculate the size of the force

applied.

11) Sean pushesStefan in hisgo-kart with a

constant force of700 newtons,

doing 5 600 joules of work.Calculate the distance travelled.

12) Darren does3 870 joules of work

when he pulls his golftrolley with a constantforce of 215 newtons.Calculate the distance Darren

pulls the trolley.

13) A horse transfers360 000 joules of

energy when it pulls aplough with a constantforce of 4 000 newtons. Calculate

the length of the furrow produced.

��Gravitational Potential EnergyAny object which is above the ground has

gravitational potential energy.

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��When an object is lifted up off theground, work is done against gravity

- The work done is equal to thei _ _ _ _ _ _ _ in the object's

gravitational potential energy. ��When an object is lowered downtowards the ground, work is done bygravity - The work done is equal to the

d _ _ _ _ _ _ _ in the object'sgravitational potential energy.

��EP = mgh Calculations14) Calculate the gravitational

potential energy of a15 kilogram cheese which is

sitting on a 1.5 metre high shelf.

16) A star (mass0.75 kilograms) sits on top of a12 metre high Christmas tree.Calculate the gravitational

potential energy of the star.

15) 'Hoot' theowl has a massof 2.8 kilograms.

Calculate hergravitational

potentialenergy whenshe is sitting

9.5 metres up atree.

17) Calculate thegravitational

potential energyof Graham's golf

ball (mass0.045 kilograms)

which is stuck1.8 metres up a tree.

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20) Kayleighhas a mass of62 kilograms.She climbs

2.5 metres upa ladder.

Determine:(a) Kayleigh's increase in

gravitational potential energy;(b) the work done against

gravity.

18) When Borisholds a set of

weights1.9 metres above

the floor, theweights have a

gravitationalpotential energy of 3 800 joules.

Calculate the mass of theseweights.

19) During a 'strongman' competition,Hamish holds a

150 kilogram boulderabove the ground.If the boulder has a

gravitational potentialenergy of 1 650 joules,

calculate its height above theground.

21) Ally theabseiler

descends35 metres down arope. His mass is

70 kilograms.Determine:

(a) Ally's decrease ingravitational potential energy;

(b) the work done by gravity.

22) Ahelicopter

(mass 6 200kilograms)increases its height above the

ground by 115 metres.Determine:

(a) the increase in gravitationalpotential energy;

(b) the work done againstgravity.

23) A skydiver (mass68 kilograms) falls

350 metres throughthe air.

Determine:(a) the decrease in gravitational

potential energy;(b) the work done by gravity.

24) When Alanaclimbs 8.5 metres

up a rope, she does4 675 joules of work

against gravity.Determine Alana's

mass.

25) When Shona,mass 66 kilograms,dives from a high

board into aswimming pool,16 500 joules ofwork is done by

gravity. Determine the distanceShona falls through.

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��Kinetic EnergyKinetic energy is movement energy.

A moving object's kinetic energy depends on itsmass and speed:

��The greater the mass of a moving object,the ___________ is the value of its kinetic energy.

��The greater the speed of a moving object,the ___________ is the value of its kinetic energy.

Kinetic energy, mass and speedare related by the formula:

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26) Quasim, whohas a mass of

60 kg, is jogging ata speed of 5 m/s.

Calculate Quasim'skinetic energy.

27) Calculate the kinetic energyof a 0.12 kg arrow which is

travelling through the air with aspeed of 50 m/s.

28) Kevin's kitehas a mass of0.02 kg. It is

travellingthrough the airwith a speed of 3 m/s. Calculatethe kinetic energy of the kite.

29) Ryan throws apaper aeroplane

of mass 0.001 kg.The plane leaveshis hand with aspeed of 5 m/s.

Calculate the kinetic energy ofthe plane at this instant.

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30) Dominiquehas a mass of55 kg. During

hergymnasticsdisplay, she

springs off theend of a beam

with a speed of 4 m/s.Calculate the kinetic energy of

Dominique at this instant.

31) Ross firesa 0.002 kg

stone from acatapult. If thestone leavesthe catapult

with a speed of10 m/s,

calculate the kinetic energy ofthe stone at this instant.

32) A bullet, travelling through theair with a speed of 1 200 m/s, has

11 520 J of kinetic energy.Calculate the mass of the bullet.

33) Duncan (mass 64 kg) has 72 Jof kinetic energy while swimming

the butterfly stroke. CalculateDuncan's speed at this instant.

34) When drivenat 2.5 m/s,

Graeme's grasscutting machine

and Graemehave a kinetic

energy of 3 750 J.Calculate the combined mass of

Graeme and the machine.

36) A golf ballleaves the faceof a golf club at

40 m/s with36.8 J of kinetic

energy.Calculate the mass of the golf

ball.

35) A 1.25 kgcannonball isfired from acannon with6 250 J of

kineticenergy.

Calculate the speed at which thecannonball leaves the cannon.

37) Daniel andhis skis have a

combinedmass of 60 kg.Daniel takes offfrom a ski jumpwith a kinetic energy of 18 750 J.

Calculate his take off speed.

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Power is the amount of work done (or the amount ofenergy transferred) every second.

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Power is measured in w _ _ _ _ ( __ ).1 w _ _ _ = 1 j _ _ _ _ per s _ _ _ _ _.

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38) A crane does 30 000 joules ofwork when it lifts a load for

6 seconds. Calculate the powerof the crane engine.

39) A weightlifter does3 800 joules of work in

1.6 seconds when he lifts a set ofweights. Calculate the powerdeveloped by the weightlifter.

40) An electric motor does30 joules of work in 1.5 seconds

when it lifts a small load.Calculate the power of the motor.

41) When Lewis pulls a loadedsledge across the snow, he

transfers 24 000 joules of energyin 60 seconds. Calculate thepower developed by Lewis.

42) Simon transfers 1 125 joulesof energy when he moves hiswheelchair for 15 seconds.

Calculate the power developedby Simon.

43) When a bucket is hoisted offthe ground, 390 joules of energy

is transferred in 6.5 seconds.Calculate the power of the hoist.

��The Principle of Conservation ofEnergy

We cannot make or destroy energy- but we can transform (change) it

from one type to another.

A car crash is a good example of onetype of energy being converted

(changed) into other types of energy.

A moving car has kinetic energy. If the carcrashes into a post, the car stops moving - Thepost does work on the car, bringing it to rest.

All of the car's kinetic energy is changed mainly to: ��"energy of deformation" (crushing the bodywork)

��heat (due to friction when the bodywork is crushed) ��sound and light (sparks created when the bodywork is crushed)

50) (a) Calculate the kinetic energy of a 1 000 kg car when ithas a speed of:

(b) At which of these speeds would the car do most damage if itcrashed into a wall? _____________

(c) Explain why: _________________________________________________________________________________________________________________________________________

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44) Murray develops 375 watts ofpower while working out for

45 seconds.Calculate the work done.

45) A food blender has a powerrating of 500 watts. Calculate the

work done by the blender in15 seconds.

46) During a tug-of-war contest,Gillian develops 380 watts of

power as she tugs for12.5 seconds. Calculate the

energy transferred by Gillian.

47) An electric drill (power rating1 250 watts) transfers

18 125 joules of energy. For whattime was the drill operated?

48) For what time does Mr. Smithpush his young son's pushchair if

Mr. Smith develops a power of65 watts while transferring7 800 joules of energy?

49) A chain saw develops1 350 watts of power while doing19 170 joules of work. Calculate

the operating time of thechain saw.

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To stop a car moving, the driver applies the brakes.The kinetic energy of the car is changed mainly to

h _ _ _ energy as a result of the force of f _ _ _ _ _ _ _acting in the brakes and between the tyres and road.

The distance a car takes to stop depends on itsspeed and hence its kinetic energy.

The shape of a speed-time graph for a "stopping" car, from theinstant the driver sees an object in the road until the car stops moving,

is shown below:

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51) (a) Why can't a car driver press the brake pedal immediately hesees an object in the road? ______________________________________________________________________________________

(b) This table contains information taken from the Highway Code.The information applies to a good car with good brakes and good

tyres on a dry road with an alert driver. Complete the table:

(c) (i) What is meant by the term "thinking distance"? ______________________________________________________________________________________________________________________(ii) No matter how fast a car is travelling, the driver always takes the

same time to react and press the brake pedal - So why does the"thinking distance" increase as the speed of the car increases?

__________________________________________________________________________________________________________________________________________________________________(d) (i) What is meant by the term "braking distance"? _______________________________________________________________________________________________________________________(ii) What happens to the "braking distance" as the speed of a car

increases? ___________________________________(iii) Explain this in terms of the car's kinetic energy: _________________________________________________________________________________________________________________________

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thinking distance/metres

braking distance/metres

overall stoppingdistance/ metres

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��Typical Energy Transformation CalculationsYou will need these formulae to solve the following problems.

The problems involve the transformation (change) of energy from one type to another:

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When a force moves an object through a distance,the force does work on the object.Work done = energy transferred.

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Power is the amount of work done (or the amount of energytransferred) every second.

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Any object which is above ground level hasgravitational potential energy - As an object islifted up off the ground, work is done against

gravity. As an object is lowered down towards theground, work is done by gravity.

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&5��"��A 10 W electric motor lifts a 0.5 kg mass through a height of

3.6 m. Calculate the time the motor takes to do this.Assume there is only one energy transformation (change).

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&5��"��0A brick falls from the top of a 20 m high chimney. Calculate the

speed of the brick at the instant before it hits the ground.Assume there is only one energy transformation (change).

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52) A 100 W electric motor lifts a 5 kg load through aheight of 4.5 m.

Calculate the time taken to do this.Assume there is only one energy transformation

(change).

53) Ricky (mass 55 kg) walks up a flight of stairs for10 s. His vertical height above the ground increases

by 5 m. Calculate the power developed by Rickyduring this activity.

Assume there is only one energy transformation(change).

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54) A 5 W electric motor takes 4.8 s to raise a 1.5 kg mass.Calculate the height through which the mass is raised.

Assume there is only one energy transformation (change).

55) A speedboat engine applies a constant forcewhich causes the speedboat (mass 1 000 kg) to travel

at 25 m/s over a distance of 1 250 m.Calculate the size of the constant force applied.Assume there is only one energy transformation

(change).

56) A loaded sledge of mass 80 kg travels with aspeed of 3 m/s when it is pulled across the snow by

a constant force of 60 N.Calculate the distance travelled by the sledge.


57) A constant force of 0.12 N moves a toy car ofmass 0.02 kg at constant speed a distance of

0.75 m across a floor.Calculate the speed of the toy car.


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58) Calculate the power developed by a jogger ofmass 62 kg who travels at 4 m/s for 124 s.


59) A wind-up clockwork toy of mass 0.002 kgdevelops a power of 0.001 W when it travels at a

constant speed for 4 s.Calculate the value of the constant speed.


60) An electric motor takes 12 s to pull a packing case18 m across a smooth floor with a constant force of

200 N.Calculate the power of the motor.


61) A cyclist develops a power of 300 W when sheapplies a constant force of 250 N to the pedals of her

bike over a time of 360 s. Calculate the distancethrough which the cyclist moves the pedals.


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62) Clumsy Colin drops a 1 kg brick onto his footfrom a height of 1.25 m.

Calculate the speed of the brick at the instantbefore it hits his foot.


63) A wheel drops off a helicopter which is hovering at aheight of 45 m.

Calculate the speed of the wheel at the instant before itstrikes the ground


64) A 0.5 kg cannonball is fired straight up from groundlevel with a speed of 50 m/s.

Calculate the maximum height the cannonball reaches.Assume there is only one energy transformation (change).

65) Jane the juggler throws a ball straight up in the airwith a speed of 4 m/s.

Calculate the ball's maximum increase in height aboveJane's hand.


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