Work

Work

Take g as 9.8 ms-2 or 9.8 Nkg-1

How much work is done if you push a shopping trolley with a constant force of 60N and it moves 5m in a direction parallel to the force?

A delivery driver lifts a mass of 6.5kg onto the back of a lorry 1.5m from the ground. How much work is done in this energy transfer?

How much work is done lifting a 5kg bag 1.2m and place it on the table. In your calculation you assume all the work is done against what?

How much work is done pulling a bag of rubbish 10m across a field by pulling on a string at 400 to the horizontal with a force of 250N?

A toy car has a mass of 110g and its clockwork engine exerts a force of 0.12N. Unfortunately it is not well made and its wheels are at a 130 angle to its direction of motion. What work does it do in travelling 25cm along a heavily carpeted floor?

A pyramid builder is organising his gang of acolytes to pull a large stone block up a ramp. The stone weighs 2.5t and the ramp has a height of 7m. The ramp is 15m long and the acolytes exert a force of 1.2 kN. How much work to they do? How much work is done on the stone to lift it through a height of 7m? How much work is done against friction?

An 80kg baseball player slides to a halt from a speed of 8 ms-1 in a distance of 4m. What is the average stopping force exerted on him by the ground? How much work is done on him? Where does the energy come from?

A 50g ball bearing is dropped from a height of 50cm into a tray of fine sand and embeds itself to a depth of 1.5cm. What was the average vertical force exerted on the ball bearing by the sand? How much work is done on the ball bearing?

y13 Homework

y13

Y11 Homework

Gravitational Potential Energy & Kinetic Energy

acceleration due to gravity = 9.8 m/s2

1. A car has a mass of 750 kg. Calculate its kinetic energy at the following velocities
(a) 10 m/s (b) 15 m/s (c) 20 m/s (d) 30 m/s (e) 35 m/s {NB 1 m/s =2 m p h}

2. (a) A car has a mass of 1000 kg. Calculate its KE at a velocity of 25 m/s.
(b) A train has a mass of 37 tonnes {1 tonne = 1000 kg}. If it also has a velocity of 25 m/s what is its kinetic energy ?

3. A woman has a mass of 65 kg.What is her GPE at the top of a 12 metre diving board ?

4. A cat has a mass of 6 kg. What is its GPE at the top of a tree that is 4.2 m above the ground ?

5. The Eiffel Tower is 300 m high. What is the GPE of a 100 g bird perched on the top of it ?

6. The Great Pyramid of Khufu (Cheops to the Greeks) is 146 m high. It is made of stones of mass 250 t. What is the GPE of the topmost stone ?

7. The Empire State Building is 449 m high(but this includes a 68 m TV mast).What is the GPE of a ball of mass 400 g at the top of the building (not the TV mast) ? If the ball is dropped over the side what will happen to the GPE ? What will be its speed at the instant before it hits the ground ? (Ignoring air resistance)

8. Olympus Mons is a volcano on Mars. It is 25 km high. What would be the GPE of a human of mass 50 kg on its summit ? (surface gravity = 0.38 that of Earth) Compare this with the same human standing on the summit of Everest 8534 m high.

9. The space shuttle has a mass of 80 t. Escape velocity (the velocity an object has to travel at in order to escape the earth's gravitational field) is 11 km/s. What is its KE at this speed? If all this KE is turned into GPE how high would it be ? What assumption do you have to make in your calculation.

How much energy would it take to accelerate the space shuttle to light speed (300 000 km/s). {This is not possible, also the equation you will use to calculate KE is not valid near the speed of light but it will do for this purpose} A nuclear power station produces around 500 MW
(500 000 000 J per second). How long would 100 power stations take to produce this amount of energy?
How feasible is travelling close to the speed of light?
The nearest star is about 4 light years away. How long would it take the space shuttle to get there at 11 km/s (22 000 mph)? {1 light year is the distance light will travel in 1 year}
How feasible is interstellar travel?

Y11 Homework on Forces

1. A light bulb converts 500 J of electrical energy into heat and light in
5 seconds. What is its power rating?

2. An electric kettle converts 210,000 J of electrical energy into heat energy in 1 minute. Calculate its power rating?

3. A person of weight 500 N climbs a 5m flight of stairs in 100 s. Calculate the power produced.

4. A car of mass 500 kg is driven up an incline of vertical height 5m in 5s. Calculate the power output of the engine.
[Gravitational field strength = 10 N/kg]

5. Calculate the energy transferred by a 300 W TV in 25 seconds.

6. Calculate the energy transferred by a 0.0002 W calculator in 5 minutes.

7. A hoist motor develops 500 W. It does 1000 J of work in lifting a mass. How long does it take to lift the mass?

8. A car develops 44 kW. It does 1980 kJ of work in travelling a certain
distance. How long does this take?

Hw on Velocity Time graphs

phy2 2003

6732 Unit Test PHY2

1. Resistance of lamps

V2/R OR I = 60/12 = (5 A) 1

R=(12 V x 12 V) /60 W 1

R =2.4ohm 1 total 3

Resistance variation

Lamp A: resistance of A decreases with current increase 1

Lamp B: resistance of B increases with current increase 1

Dim filament

Lamps are dim because p.d. across each bulb is less than 12 V 1

Why filament of lamp A is brighter

Bulbs have the same current 1

p.d. across A > p.d. across B/resistance A> Resistance B 1

OR

power in A > power in B 2

total 8

2 Table

Physical Quantity - Typical value

Resistance of a voltmeter -10 M ohm

Internal resistance of a car battery - 0.05 ohm

Internal resistance of an EHT supply -10 M ohm

Resistivity of an insulator - 2.0 x 10¹⁵ ohm m

Drift velocity of electrons in a metallic conductor - 0.3 mm s^-1

Temperature of a working filament bulb - 3000 K

[Mark is lost if 2 or more values are put into one box] total 6

3. Current in heating element

P= VI 1

I = 500 W / 230 V 1

I = 2.2 A 1

Or

P=V²/R 1

R= 230 x 230/105.8 1

I = 2.2A 1

Drift velocity

Drift velocity greater in the thinner wire 1

Explanation

Quality of written communication. 1

See I = nAQv 1

is the same (at all points) 1

(probably) n (and Q) is the same in both wires 1 total 8

4 Resistance of films

R= pl/A 1

R = pl/wt or A = wt 1

Resistance calculation

R = (6.0 x 10^-5) (8 x 10^-3 m) / (3 x 10^-3m) (0.001 x 10^-3 m) 1+1

(Correct substitution but values in mm 1)

R= 160 ohm 1 ecf if in mm

Resistance of square film

L=w 1

R= pl/lt=p/t 1

R= pw/wt=p/t 1

Total 7

5. Definition of specific heat capacity

energy (needed) 1

(per) unit mass/kg and per unit temperature change K or C 1

OR

Correct formula [does not need to be rearranged] 1

with correctly defined symbols 1

Circuit diagrams (see end)

Accept voltmeter across heater and ammeter as well as voltmeter across heater only

Means of varying p.d./current 1

Voltmeter in parallel with a resistor symbol 1

Ammeter in series with any representionof a heater. 1

Other apparatus

(Top pan) balance / scales 1

Stopwatch / timer / clock 1

Explanation

Energy/heat loss to surroundings/air/bench 1

OR

Mc delta T +delta,Q = VIt or equivalent in words (e.g. student ignores energy loss in calculations) 1

Modifications

Any two from

Use of insulation around block

Ensure all of heater is within block

Grease heater/thermometer

Total 10

Specific Heat Capacity Calculation

C = delta Q/ m delta T = (860 x 10³)/ (1.4 kg) (750 – 22) = 844 (J kg ^–1 K^-1)

Conversion of kJ to J 1

Subtraction of temp 1

Answer 1

Energy transfers diagram

Label 2 (energy to) (warm) water (and trough) 1

Label 3 (energy used to) evaporate water / cause evaporation/latent heat/change of state 1

Total 5

Gas equation

PV = nRT [Accept symbols or words] 1

Molar gas constant unit

R= PV/nT

P – kgm^-1 s 1

V – m³ T– K n – mol all three for 1

Kinetic energy of molecule

Nm =M

density = Nm²>/3V correctly combined the 2 equations 1

Nm²> = 3nRT density = any mass –: volume 1

Show that

Kinetic energy =m²>/2=(3/2)n(RT/N) 1

Sketch graph

PV on y axis Temperature/’C on x axis

[accept axes reversed and correct graph] 1

Straight line graph with negative intercept 1

Gradient R 1

Intercept at – 273 ’C 1

[All these marks can be scored on graph)

total 10

8. Definition of e.m.f. of a cell

work/energy (conversion) per unit charge 1

for the whole circuit / refer to total energy 1

OR

Work/energy per unit charge 1

converted from chemical to electrical (energy) 1

OR

E = W/Q for whole circuit 1

All symbols defined 1

OR

E = P/I for whole circuit 1

All symbols defined 1

[Terminal p.d, when no current drawn scores 1 mark only] 2 max

Circuit diagram

See top

R 1

A in series 1

R (can be variable) 1 A and V correct 1 V as shown

Or across R+ A

Or across battery

[2nd mark is consequent on R(fixed, variable )or lamp]

Sketch graph

See top

Graph correctly drawn with axes appropriately labelled and consistent with the circuit drawn 1

Intercept on R axes equivalent to( – )r and Gradient equivalent to ( – )r [Gradient mark consequent on graph mark] 1

[Gradient may be indicated on graph]

Grade boundaries

A 41 B 37 C 33 D 26 E 25

phy1 2003

6731 Unit Test PHY1

1. Magnitude of resultant force

4 cm line S / 1.7 cm line N 1

8 cm line NE / 8N resolved into two perp. components (5.7E & 1.7N or 5.7N) 1

Correct construction for vector sum 1

5.7 – 6.1 N 1

Name of physical quantities

Vectors 1

Two other examples

Any two named vectors other than force (if >2, must all be vectors) 1

2. Calculation of average velocity

Use of v = s/t 1

v = 1.86 m s -1 / 1.9 m s -1 1

Acceleration of trolley

Selecting u = u + 2as 1

Correct substitutions 1

2.87 m s /2.9 m s /3.0 m s-1 1

Tension in string

Use of F = ma 1

2.73 N / 2.76 N / 2.85 N 1

Assuming no action other horizontal force/table smooth/light string/inextensible string 1

Explanation

Suspended mass/system is accelerating 1

Idea of resultant force on the 0.4 kg mass 1

4. Addition to diagram

Downwards arrow Y through middle third of left leg 1

Downward arrow Z with correct line of action 1

[Ignore lengths of arrows and point of action] [Must have at least one correct label to get 2 marks; no labels gets max 1 out of 2] [One correct label can get 2 marks]

Explanation

Quality of written communication

Clockwise moments = Anticlockwise when balanced

Y is smaller than X but acts further from P

Moment of XP /Moment of Y = F x YP

Z has little or no moment about P/Z acts through P

Gravitational potential energy

Use of mgh 1

Vertical drop per second = (8.4 m) sin (3) 1

-.9 x 10 J/Js -1/W 1

What happens to this lost gpe

Becomes internal energy/used to do work against friction and or heat energy. 1[mention of K.E. loses the mark]

Estimate of rate at which cyclist does work

Rate of working = 2 x 3.9 x 10 W 1

=7.8 to 10 W 1

[3.9 x 10 W earns 1 out of 2]

6. Momentum and its unit

Momentum = mass x velocity 1

Kgms-1 or N s 1

Momentum of thorium nucleus before the decay

Zero 1

Speed of alpha particle/radium nucleus and directions of travel

Alpha particle because its mass is smaller/lighter 1

So higher speed for the same (magnitude of) momentum OR Newton 3rd Law argument 1

Opposite directions/along a line 1

Nuclear equation

Correct symbol and numbers for tin OR beta 1

Correct symbols and numbers for the other two 1

Decay constant

Use of lambda = 0.69/ half life 1~

1.57 x 10^-15 y-1 OR 4.99 x 10 s-1 1

Activity of source and comparison with normal background count

rate

Use of A = lambda N 1

0.11/0.12 (Bq) 1

Lower (than background) [Allow ecf – assume background = 0.3 to 0.5] 1

8. Radiation tests

Alpha:

Test 2 or 2 and 1 1

Count drops when alphas have been stopped by the air / alphas have a definite range / (only) alpha have a short range (in air) 1

Beta:

Test 3/3 and 1, because 1 mm aluminium stops (some) beta/does not stop any gamma rays 1

Gamma:

Test 4 or 4 and 1, because 5 mm aluminium will stop all the betas, (so there must be gamma too)/gamma can penetrate 5 mm of aluminium

Table

Target for Alpha scattering

Gold atoms/gold foil gold leaf/gold film/very thin sheets of gold/metal foil etc. [NOT thin gold sheet] 1

Target for Deep inelastic scattering Protons/neutrons/nucleons /liquid hydrogen/nuclei 1

Conclusions

(i) Atom mainly empty space/nucleus is very small 1

Nucleus dense/massive 1

(ii) Nucleons have a substructure 1

Made of quarks 1

Phy2 2002

June 2002 PHY1

1.

C 1

A 1

B 1

E 1

2. Composition of alpha article

2 protons + 2 neutrons only 1

Explanation of ionize

Change nunber/Add/Remove electrons 1

Estimation of time alpha article would take to travel

Use of E = ½ mv2 1

Use of t = diameter/u 1

6.3 x 10^-18 s [ no ecf] 1

Explanation comparing speed of alpha and beta articles

Faster 1

Less massive/lighter/less weight (not smaller) 1

3. Explanation of essential difference between 2 definitions

Distance in direction of force against distance perpendicular to force 1

Correctly identifying which is which 1

Principle of moments

AP =80

,PB=32

[allow+ 1 ] [no ue ] 1

Demonstrate that moments are = equal. [allow any distance values] 1

Distance load at B raised

Use of work = force x distance / use of rngh [ beware m = 20 ] 1

Use of work out = work in / use of mgh lost = mgh gained 1

2.4x10 m 1

OR

Similar triangles/distance moved proportional to distance from pivot 1

x/6 x 10^-3 = 32/80 or equivalent 1

2.4x 10 m 1

4. Deceleration of cars

Acceleration = gradient / suitable eqn. of motion. 1

Correct substitutions [ 0.9 for t is wrong] 1

6.1 – 6.3 m s2[-ve value – 1] [ no ecf ] 1

Area under velocity -time graph

Distance/displacement 1

Shaded area

6.9 – 7.5 1

m 1

[Allow 1 mark for 5.5 – 6.1 cm .]

Minimum value of the initial separation

Both sloping lines continued down to time axis [by eye] 1

Explanation

Area between graphs is larger/B travels faster for longer/B still moving when A stops 1

Extra distance B goes is larger/ > 7.2 1

Initial separation must be larger 1

5. Experiment

2 light gates 1

Gate gives time trolley takes to pass [ not just ’the time’] 1

Speed = length of ’interrupter’/time taken 1

Or

2 ticker timers 1

dots at known intervals 1

speed = lenghth of tape / time taken 1

(ruler and clock method 1 mark max)

Total momentum of trolleys

Zero 1

It was zero initially or momentum is conserved [consequent] 1

Speed v of A

Use of momentum = mass x velocity 1

Use of mass x speed (A) = mass x speed (B) 1

1.8 m s -1 [ignore – ve signs] 1

6. Explanation of why kicking a door is more effective

Quality of written communication 1

Foot decelerates/ loses momentum 1

This takes place rapidly giving a large force by Newton 2 or equation versions [consequent] 1

Door is providing this force [consequent on mark 1] 1

Door acts on foot; by ’Newton 3’ foot acts on door 1 Max 3

7. Free-body force diagram

Normal reaction/contact force [or Nor R or push of table] upwards 1

E-M magnetic force [or magnetic attraction or pull of magnet] to right 1

Weight [or W or mg or gravitational force or gravitational attraction or pull of Earth] downwards 1

[Ignore labeled forces of action or drag] [if unlabeled – 1 each force]

Forces

Pull on earth 1

Upwards [consequent] 1

Or

Push contact / force on table 1

Downwards 1 [consequent]

Or

Force on magnet X 1

To left [consequent] 1

Precautions

Measure background radiation //shield apparatus 1

Subtract it off/ because it may vary//to eliminate background 1

Repeat the count and average 1

Because count (or emission) is random/varying 1

Source the same distance from GM on both occasions 1

Because count rate varies with distance 1 Max 3

[NB Marks must come from any TWO precautions.]

Ratio

0.88 or l. 1 [min. 2 sf] [not%] 1

Count for year 3

11 994 1

Graph

Suitable axes and scales [don’t award if factors 3, 7 used][not Bq] 1

Correct plotting of points 1

Use of curve and halving count rate 1

5.3 to 5.4 yr 1

9. Name of nuclei

Isotopes (not radioisotopes) 1

Nuclear equation

Electron numbers complete anywhere 1

Correctly balanced 1

Densest material

Sn 115 1

phy2 june 2007

Synoptic Summer 2007

y12 Physics

Resistivity
A coil of constantan wire of length 2 m has an area of cross-section of
7 x 10-7 m2. If its resistivity is 49 x 10-8 Ω m, find its resistance.

A coil of wire 4 m long has a resistance of 20 Ω. If its resistivity is
108 x 10-8 Ω m, find its area of cross-section.

A 1.75 m length of tin wire with a diameter of 0.70 mm is found to have a resistance of 0.5 Ω Find the resistivity of tin.

A resistor of 2 Ω is to be made from manganin wire of resistivity
42 x 10-8 Ω m having a diameter of 0.42 mm. What length is required?

Find the resistance of a wire 2.8 m long with a resistivity of 22 x 10-8 Ω m and a diameter of 0.56 mm.
A wire has a resistance of 2 Ω Find the resistance of a wire of the same material which is three times as long, but with half the diameter.

y11 Triple Sciecnce

Electro Statics


Explain the following:

1) Nylon clothing crackles as you undress.
2) In dry weather, people walking on clean carpets may a shock if they touch a radiator
3) Passengers sliding off a car seat on to the ground sometimes get a shock
4) Petrol road tankers usually have a length of metal chain hanging down to touch the ground.
5) A rubbed balloon will stick to the wall for some time
6) A mirror or window polished by a dry cloth on a dry day may become dusty.
7) As sellotape is pulled of a roll it is attracted to your hand.
8) When spraying an object with paint, less paint is wasted if the object is charged
9) A TV screen becomes dusty
10) The amount of smoke leaving a factory can be reduced by placing a charged object in a chimney

y8 Joule

Weathering of the Elms

The oldest part of The Elms was built in 1735 for Sir Joseph Ayloffe. When it was built Acton was a small country village surrounded by fields.
How old is The Elms?
Describe the changes that have occurred in Acton since the Elms was built.

In contrast the Sports Hall was built in 1994.

We are going to look at the state of bricks in the two buildings.

The Elms

Some of the brickwork has been replaced so you must try and find an original brick.

Sketch the brick that you have chosen below.
Label features such as small holes and cracks. Is there any evidence of plant life such as moss or green/grey crusty lichens?
Look at other bricks, are they similar to the one you have drawn. Are there other features that you think are worth mentioning? Is the wear more noticeable parts of the building more exposed to the weather.

If there is time you can sketch another brick from the north side of the building.

The Sports Hall

Are any of the features seen in the bricks on The Elms visible in the bricks of the sports hall?

What reasons can you think of for the differences?
When The Elms was new do you think the bricks looked as they do now?
What could account for the change in surface of the bricks in the Elms?

Keywords

Chemical weathering, abrasion, smooth, rough, surface, cracks, flakes, breaking off, ice, snow, wind, sun, rain, heat, expansion, contraction