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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

if three forces F1.f2 .f3 act at a point on a Cartesian plane in the daigram .....so if the question says write down the x and y components ..... I really don't understand
Syamthanda Reply
hey , can you please explain oxidation reaction & redox ?
Boitumelo Reply
hey , can you please explain oxidation reaction and redox ?
Boitumelo
for grade 12 or grade 11?
Sibulele
the value of V1 and V2
Tumelo Reply
advantages of electrons in a circuit
Rethabile Reply
we're do you find electromagnetism past papers
Ntombifuthi
what a normal force
Tholulwazi Reply
it is the force or component of the force that the surface exert on an object incontact with it and which acts perpendicular to the surface
Sihle
what is physics?
Petrus Reply
what is the half reaction of Potassium and chlorine
Anna Reply
how to calculate coefficient of static friction
Lisa Reply
how to calculate static friction
Lisa
How to calculate a current
Tumelo
how to calculate the magnitude of horizontal component of the applied force
Mogano
How to calculate force
Monambi
a structure of a thermocouple used to measure inner temperature
Anna Reply
a fixed gas of a mass is held at standard pressure temperature of 15 degrees Celsius .Calculate the temperature of the gas in Celsius if the pressure is changed to 2×10 to the power 4
Amahle Reply
How is energy being used in bonding?
Raymond Reply
what is acceleration
Syamthanda Reply
a rate of change in velocity of an object whith respect to time
Khuthadzo
how can we find the moment of torque of a circular object
Kidist
Acceleration is a rate of change in velocity.
Justice
t =r×f
Khuthadzo
how to calculate tension by substitution
Precious Reply
hi
Shongi
hi
Leago
use fnet method. how many obects are being calculated ?
Khuthadzo
khuthadzo hii
Hulisani
how to calculate acceleration and tension force
Lungile Reply
you use Fnet equals ma , newtoms second law formula
Masego
please help me with vectors in two dimensions
Mulaudzi Reply
how to calculate normal force
Mulaudzi
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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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