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Key equations

Time dilation Δ t = Δ τ 1 v 2 c 2 = γ τ
Lorentz factor γ = 1 1 v 2 c 2
Length contraction L = L 0 1 v 2 c 2 = L 0 γ
Galilean transformation x = x + v t , y = y , z = z , t = t
Lorentz transformation t = t + v x / c 2 1 v 2 / c 2
x = x + v t 1 v 2 / c 2
y = y
z = z
Inverse Lorentz transformation t = t v x / c 2 1 v 2 / c 2
x = x v t 1 v 2 / c 2
y = y
z = z
Space-time invariants ( Δ s ) 2 = ( Δ x ) 2 + ( Δ y ) 2 + ( Δ z ) 2 c 2 ( Δ t ) 2
( Δ τ ) 2 = ( Δ s ) 2 / c 2 = ( Δ t ) 2 [ ( Δ x ) 2 + ( Δ y ) 2 + ( Δ z ) 2 ] c 2
Relativistic velocity addition u x = ( u x + v 1 + v u x / c 2 ) , u y = ( u y / γ 1 + v u x / c 2 ) , u z = ( u z / γ 1 + v u x / c 2 )
Relativistic Doppler effect for wavelength λ obs = λ s 1 + v c 1 v c
Relativistic Doppler effect for frequency f obs = f s 1 v c 1 + v c
Relativistic momentum p = γ m u = m u 1 u 2 c
Relativistic total energy E = γ m c 2 , where γ = 1 1 u 2 c 2
Relativistic kinetic energy K rel = ( γ 1 ) m c 2 , where γ = 1 1 u 2 c 2

Conceptual questions

How are the classical laws of conservation of energy and conservation of mass modified by modern relativity?

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What happens to the mass of water in a pot when it cools, assuming no molecules escape or are added? Is this observable in practice? Explain.

Because it loses thermal energy, which is the kinetic energy of the random motion of its constituent particles, its mass decreases by an extremely small amount, as described by energy-mass equivalence.

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Consider a thought experiment. You place an expanded balloon of air on weighing scales outside in the early morning. The balloon stays on the scales and you are able to measure changes in its mass. Does the mass of the balloon change as the day progresses? Discuss the difficulties in carrying out this experiment.

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The mass of the fuel in a nuclear reactor decreases by an observable amount as it puts out energy. Is the same true for the coal and oxygen combined in a conventional power plant? If so, is this observable in practice for the coal and oxygen? Explain.

Yes, in principle there would be a similar effect on mass for any decrease in energy, but the change would be so small for the energy changes in a chemical reaction that it would be undetectable in practice.

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We know that the velocity of an object with mass has an upper limit of c . Is there an upper limit on its momentum? Its energy? Explain.

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Given the fact that light travels at c , can it have mass? Explain.

Not according to special relativity. Nothing with mass can attain the speed of light.

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If you use an Earth-based telescope to project a laser beam onto the moon, you can move the spot across the moon’s surface at a velocity greater than the speed of light. Does this violate modern relativity? (Note that light is being sent from the Earth to the moon, not across the surface of the moon.)

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Problems

What is the rest energy of an electron, given its mass is 9.11 × 10 31 kg ? Give your answer in joules and MeV.

0.512 MeV according to the number of significant figures stated. The exact value is closer to 0.511 MeV.

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Find the rest energy in joules and MeV of a proton, given its mass is 1.67 × 10 27 kg .

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If the rest energies of a proton and a neutron (the two constituents of nuclei) are 938.3 and 939.6 MeV, respectively, what is the difference in their mass in kilograms?

2.3 × 10 30 kg ; to two digits because the difference in rest mass energies is found to two digits

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Questions & Answers

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the study of living organisms and their interactions with one another and their environments
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Victoria Reply
HOW CAN MAN ORGAN FUNCTION
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the diagram of the digestive system
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allimentary cannel
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How does twins formed
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They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
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Genetics is the study of heredity
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discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
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the study of living organisms and their interactions with one another and their environment.
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discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
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what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
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cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
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cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
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cell is the building block of life.
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Practice Key Terms 4

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Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
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