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20 Cards in this Set
- Front
- Back
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Momentum (p)
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measure of a moving object's tendency to continue along its present path
p = mv p: momentum m: mass v: velocity Units are kg m/s closely related to inertia 1. in an isolated system, momentum is always conserved 2. momentum is a vector initial momentum of an isolated system is always equal to final momentum in magnitude and direction M1V1 = M2V2 |
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Elastic collisions
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mechanical energy is conserved
no energy dissipates to internal energy example is atomic collisions only conservative forces are at work, resulting in conservation of mechanical energy sum of mechanical energies before collision equals sum of mechanical energies after collision Uinitial + Kinitial = Ufinal + Kfinal |
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Inelastic collisions
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colliding objects lose some mechanical energy to internal energy
must use conservation of momentum to solve inelastic collision probelms Pinitial = Pfinal completely inelastic collision is when the colliding objects stick together upon collision M1V1 + M2V2 = (M1+M2)V3 Px (initial) = Px (final) Py (initial) = Py (final) |
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Reverse collisions
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Objects start together and suddenly burst apart
Final and initial momentum are equal Example is explosion or radioactive decay where species start from rest in a 2 piece explosion, 2 pieces must separate in exactly opposite directions because of vector nature of momentum M3V3 = M1V1 + M2V2 M1V1 = M2V2 |
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Impulse (J)
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equal to change in momentum
J = change in momentum Force during time of collisions is not constant Average force: J = (Favg)(change in time) Change in p = (Favg)(change in t) If time over which collision occurs is increased, than force is decreased |
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Machines
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mechanical devices that reduce force when doing work
ideal machines reduce force but don't change work nonideal machines increase work because they increase internal energy through friction 3 machines: 1. ramp 2. lever 3. pulley |
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Ramp
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an inclined plane
type of machine W = mgh W: work m: mass g: gravity h: height F = mgsin0 fraction by which we reduce the force must be equal to fraction by which we increase the length of the ramp work is not changed |
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Lever
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based on principle of torque
type of machine increases distance through which force acts clockwise torque must equal counter-clockwise torque T = Fl T: torge F: force l: lever arm work is not changed |
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Pulley
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based on principle of ramp and lever
allows force to act on a greater distance and thus do same amount of work with less force tension through a massless rope attached to a frictionless, massless pulley is constant tension is the same at every point in the rope |
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Radioactive Decay
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concerns atoms that spontaneously break apart
hydrogen does not undergo spontaneous decay No atoms with more than 83 protons are considered stable 5 types: 1. alpha decay 2. beta decay 3. positron emission (beta decay) 4. gamma ray production 5. electron capture (beta decay) |
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Half-life
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predictable rate of decay of any substance (large group of identical atoms)
length of time necessary for 1/2 of given amount of substance to decay 4 variables: 1. initial amount of substance 2. final amount of substance 3. number of half-lives (time period/half-life) 4. length of half-life |
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Alpha decay
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alpha particle is a helium nucleus = 2 protons and 2 neutrons
an alpha particle is lost mass number (A) decreases by 4 atomic number (Z) decreases by 2 |
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Beta decay
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expulsion of an electron
beta particle is an electron or a positron (an electron with a positive charge) not the destruction of an electron, instead it is the creation of an electron and a proton from a neutron and the expulsion of the newly created electron mass number (A) doesn't change atomic number (Z) increases by 1 |
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Positron emission
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type of beta decay
emission of a positron when a proton becomes a neutron a proton is transformed into a neutron and a positron is emitted mass number (A) doesn't change atomic number (Z) decreases by 1 |
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Electron capture
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capture of an electron along with the merging of that electron with a proton to create a neutron
a proton is destroyed and a neutron is created mass number (A) doesn't change atomic number (Z) decreases by 1 |
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Gamma ray production
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high frequency photon
has no charge and doesn't change the identify (atomic number, Z) of the atom from which it is given off often accompanies other decay types when an electron and a positron collide mass number (A) doesn't change atomic number (Z) doesn't change matter-antimatter collision (annihilation), where mass is destroyed releasing energy in the form of gamma rays |
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Rest mass energy
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E = mc^2
E: energy m: mass created or destroyed c: speed of light (3e^8 m/s) latent energy within the mass of an object use when mass is created or destroyed |
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Mass defect
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difference in masses before and after creation or destruction of mass
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Fusion
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combining of 2 nuclei to form a single heavier nucleus
binding energy increases, new bonds are more stable and stronger large amount of energy is released, energy comes from mass defect more energy was released in formation of stronger bonds than was absorbed in breaking of weaker bonds |
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Fission
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splitting of single nucleus to form 2 lighter nuclei
large amount of energy is released, energy comes from mass defect |
