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21 Cards in this Set
- Front
- Back
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Momentum
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p; measure of a moving object's tendency to continue along its present path
p=mv (kg m/s) in an isolated system, momentum is always conserved momentum is a vector |
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Collision type depends on...
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whether bodies colliding follow hooke's law perfectly (and all E is transfered back to the motion of the bodies) or not (some E is lost, dissipated as internal E)
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Elastic collisions
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sum of mechanical E before collision equals sum mechanical E after the collision
Ui + Ki = Uf + Kf |
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Inelastic collisions
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some mechanical E is lost to internal E
need to set momentums equal p initial = p final split in x and y directions |
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reverse collision
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two objects start together and suddenly burst apart
final and initial p must be zero, must separate in exactly opposite directions |
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Impulse
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equals change in momentum
force during time of contact is not constant therefore AVG force is J=Favg change in t=change in m v |
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Machines
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mechanical devices that REDUCE FORCE when DOING WORK
IDEAL machines reduce force but DONT change work NONideal - increase work because they increase internal energy through friction ramp lever pulley hydraulic lift |
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Ramp
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fraction we want to reduce the force is the same as the fraction by which we INCREASE the length of the ramp
think W held constant = Fd |
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Lever
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like ramp, lever allows us to increase the distance through which our force acts
sometimes levers look like pulleys... check width of pulley and if force is acting on either side (like lever through middle) |
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Pulley
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remember that tension throughout a massless rope attached to a frictionless, masseless pulley is constant = T is same at every point in rope
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radioactive decay
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atoms that spontaneously break apart
atoms with high decay = radioactive no atoms with more than 83 protons are considered stable neutron:proton stability: small atoms 1:1 larger atoms 1.5:1 |
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half life problems
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involve ONLY 4 variables:
initial amt substance final amt substance number of half lives (often given as period, divide by length of half life) length of half life will provide with 3 and ask for 4th count off on fingers |
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types of radioactive decay
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alpha decay (helium nucleus: 2 prot and 2neut)
beta decay (expulsion e-) positron emission (proton to neutron=positron and emitted) electron capture (electron plus proton = neutron) gamma ray (high freq photon, doesnt change identity of atom, just is energy release when mass is destroyed) |
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Mass defect
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E=mc2
"latent energy within the mass of an object" - only see if mass created or destroyed c=3x10^8m/s binding energy holding nucleons in nucleus together will be the mass defect (mass turned to E to hold together) |
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Fusion
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combining of 2 nuclei to form single heavier nucleus - comes from mass defect
most stable nuclei have strongest binding energy |
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fission
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splitting of a single nucleus to form two lighter nuclei
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alpha decay
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alpha particle is a helium nucleus = 2 protons and 2 neutrons
4 a 2 |
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beta decay
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expulsion of electron
beta particle is electron OR positron (e+) it is actually the creation of an electron and a proton from a neutron, and new electron is expelled 0 e -1 |
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Positron emission
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emission of positron when proton becomes a neutron
0 e 1 |
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electron capture
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merging of captured electron with proton to create a neutron
therefore proton destroyed, neutron created 201/80 Hg + 0/-1 e --> 201/79 Au + 0/0 gamma |
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gamma ray
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high frequency photon
doesn't change identity of atom from which it is given off usually accompanies other decay types ie when e- and e+ collide = get 2 0/0 gammas = annihiliation |
