Paper 1 And Paper 2Paper 1 And Paper 2

Math- the language of Physics – A lot of Calculation

SI Units – International System – But American likes to use their system

AWS Questions Sets can be in S.I or in Imperial Unit

Quantity Unit SymbolLength meter m

Mass kilogram kg

Temperature kelvin K

Time second s

Amount of Substance mole mol

Luminous Intensity candela cd

Electric Current ampere a

Quantity unit SymbolVolume cubic meter m3

Density kilograms per cubic meter

kg/m3

Speed meter per second m/s

Newton kg m/ s2 N

Energy Joule (kg m2/s2) J

Pressure Pascal (kg/(ms2) Pa

Name Symbol Value

gigameter Gm 109

megameter Mm 106

kilometer km 103

decimeter dm 10-1

centimeter cm 10-2

millimeter mm 10-3

micrometer μm 10-6

nanometer nm 10-9

picometer pm 10-12

Say you want to simplify; 5,000Km You can write it as 5 x 103 Km Or 5E+3Km (E+3=103)

Or Even Better As 5Mm ………….

wonder why American still insist on Imperial usage..When they lost billions in Mars Orbital Satellite Program….

Identify the smallest and the largest measurement from the following;

A) 2.15 X10-2cm B) 2.15 X 1010 µm C) 5 X 10-3Km D) 5 X 1010 nm

1) Convert the 100cm2 to m2 unit?

2) Convert 1m2 to cm2 unit?

3) The density of water is 1.05gcm-3 express the density in unit Kgm-3

What From To Factor

Acceleration ft/s2 m/s2 Multiply by 0.3048

Area ft2 m2 Multiply by 9.2903

Energy BTU Joule Multiply by 1.05435 X 103

Force lbf N 4.44822

Stress (Pressure)

lbf/ft2 Pa(N/m2) 4.788X 101

Temperature Celcius ºC Kelvin (K) C + 273

Temperature Fahrenheit ºF

Kelvin (K) 5/9 (F + 459.67)

1) Convert 200ft2 to m2

2) What is the value when Fahrenheit is equal to Kelvin (K)?

Mass = Kg

Volume = m3 = Area (m2) X Height (m)

Density = Mass (Kg) / Volume (m3)

1)The standard kilogram is a platinum–iridium cylinder 39.0 mm in height and 39.0 mm in diameter. What is the

density of the material?

Answer : 2.15 X 104 kg/m3

2) What mass of a material with density & is required to make a hollow spherical shell having inner radius r1 and outer radius r2?

Answer : 4Л ρ (r23 – r13)/3

Force = Mass (Kg) X Acceleration (ms-2) ; Unit : Kgms-2@Newton, N

Work = Force (N) X Displacement (m) ; Unit : Kgms-2 @ Nm @ Joule, J

Power = Work / time taken Unit : Kgms-2/s = Kgms-3 @ J/s @ watt, W

Hooke’s Law ;

F= KX

where K is spring constant and X is spring displacement.

**Energy is transferred from one object to another when work is done.

A welding set is rated at 500 watts. (a) What is the cost of operating the welding set

for 5 hours if the utility charges $1.5 per kilowatt-hour?

(b) How many joules of energy are purchased?

Answer : a) $3.75 b) 9M joules

( cos )W F x cos 0 1

cos 90 0

cos180 1

Accelerating a Crate

The truck is accelerating ata rate of +1.50 m/s2. The massof the crate is 120-kg and itdoes not slip. The magnitude ofthe displacement is 65 m.What is the total work done on the crate by all of the forces acting on it?

Answer : 1.2 x 104 Joule

Find the work done if Ө = 50, Force applied is 45N and displacement is 75m

Answer : 2170 J

Principle of conservation energy;

Energy cannot be created nor destroyed, it can be transformed from one form to another but the total energy in a system is constant.

Work done = Energy Required Energy = Work done

Forms of Energy:Chemical – Nuclear – Radiant – Thermal – Sound –

Electrical - Mechanical

Definition: Kinetic Energy The kinetic energy of an object with mass m and speed v is

The SI Unit for Kinetic Energy is joule (J).

221 mvKE

• Potential Energy :The work done by the force of gravity on an object is:

• This is equal to the gravitational potential energy PE that an object has by virtue of its position relative to the surface of the earth, or energy stored by spring.

• That position is measured by the height h of the object relative to an arbitrary zero level.

mghPEg 2

2

1kxPEs

Daredevil Jumping

A motorcyclist attempts to leap a canyon by driving horizontally off a cliff. Initial velocity is 38m/s and heights from one hill to another its as in picture. Calculate the velocity when it reach second hill. Answer : 46.16m/s

Force is in equilibrium (static) when sum of all forces is zero.

ΣFx = 0 ΣFy = 0 ΣFz = 0

mg

T1

mIf mass m is 100lb, calculate T1 needed to hold it from falling down. Ө = 45 and g =32.8ft/s2

Answer: 1690.49 lbf ( )Figure 1

Referring to figure 1, if now the mass is 200 lb and T1 acted on the mass is 2000 lbf what happened to the part now?

a)Move downward?b)Move upward ?c)Not moving (static)

Answer = B

Calculate work done on the car below if coefficient of resistance between tires and road is µ=0.25, S =2m, F is 200KN and car mass is= 500Kg

Answer : 397.5Kj

Fr

Q = mC.Ө

Where C is specific heat capacity of liquid or solid. C JKg-1⁰C-1 or JKg-1⁰K-1

Heat capacity of an object is the quantity of heat energy required to increase its temperature by 1ºC or 1k

Q is heat energy. Joule Ө is temperature difference Q is heat gain if Ө is positive and heat loss if Ө is

negative. m is mass of the object.

1) The temperature of 10 Kg of a substance rises by 55ºC when heated. Calculate the temperature rise when 22Kg of the substance is heated by the same quantity of heat.

Answer = 25ºC

2) Aluminium, C is 900Jkg-1ºC-1 ,and melting temperature of Aluminium is 1400ºC, estimate energy needed for welding to take place, if surrounding temperature is 24ºC? ..Assume C is constant throughout the temp diff.

Answer : 1.2MJ per 1Kg

Specific latent heat is the quantity of heat energy required to change 1Kg substance phase i.e liquid to gas , solid to liquid.

Q =mL

Where Q= energy heat; J

m = mass

L = Specific latent heat in joule/kg

1) What is the heat required to change 1.2Kg of ice at -5⁰C to the water at 30⁰C?

Answer = 567000J

2) Assuming above process was done with the help of heater rated at 300W, what is the time needed to complete the temperature change?

Answer = 31.5 minutes.

Thermal Conductivity

thermal conductivity, k, is the property of a material reflecting its ability to conduct heat.

The Fourier’s Law use thermal conductivity value to calculate heat conducted or can be said as heat losses due to conduction.

A higher K value means a better conductor., or how well the materials conduct heat.

q k

dTdx

dx

dTkAQ

heat flux(J/m2-s) or (watt/m2)

heat flux(J/s) or watt

thermal conductivity (J/m-K-s) or (J/m-⁰C-S)

Cross section area of conduction medium

temperature

gradient per length

heat flux = heat transfer

“-” is because T2-T1

Looking at the table below suggest which material

is suitable candidate for quick heating pot, conductor and insulators and explain why ?

Material

Specific H eat Capacity JKg-1⁰K-

1

Thermal Conductivity J/mKs

A 900 240

B 450 79

C 390 390

D 380 110

Quick Heating Pot; D because it has a low specific heat capacity which mean it require less heat to raise to a particular temperature.

Conductor : C because it has the highest thermal conductivity which mean it can transfer heat better than other materials.

Insulator : B because it has the lowest thermal conductivity value which mean it doesn’t transfer heat well.

Thermal ExpansionThermal Expansion

When temperature rises molecules have more kinetic energy

» they are moving faster, on the average consequently, things tend to expand

amount of expansion depends on… change in temperature original length coefficient of thermal expansion

» L0 + L = L0 + L0 T

L = L0 T (linear expansion)

V = L0 T (volume expansion)

Temp: T

Temp: T+T

L0

L

Coefficient of thermal expansion. α or CTE

1) As you heat a block of aluminum from 0 C to 100 C its density 1. Increases 2. Decreases 3. Stays the same

Answer : Decrease, Volume increase resulted decreases in density.

T = 0 C

M, V0

0 = M / V0

T = 100 C

M, V100

100 = M / V100

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