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June 9, 2009 Bluff
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What are the units for: work, power, energy? Work = joule (J) Power = watt (W) Energy = joule (J)
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What is the power exerted when 3000 mJ of work is done in 2 s? P = W t W = 3000 mJ x 1 J - 1000 mJ P = 3 J = 1.5 W 2 s
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How much work is done when a 320 N box is pushed 6 m? W = F x d W = (320 N) x (6 m) W = 1920 J
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What type of energy is food? What is it transformed into after you eat it? Chemical Potential and kinetic
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Why are machines not 100% efficient? Friction causes energy to be “lost” as heat (thermal energy)
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What is the potential energy of a 5 N object that is 3 m off the ground? PE = w x h PE = (5 N) x (3 m) PE = 15 J
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What is the mass of an object with 5 kJ of potential energy at a height of 25 m? m = PE - (g x h) PE = 5 kJ x 1000 J = 5000 J 1 kJ m = (5000 J) = -20.4 kg (9.8 m/s 2 x 25 m)
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Name a device that transforms electrical energy into useful heat energy. Hair dryer Toaster Heater
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Name a device that turns chemical energy into mechanical energy. Car Toys with batteries Battery powered fans Your body (food!)
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Name an object that converts chemical energy into light energy. Flashlight Glowstick Headlights of car
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What must be true about the energy into a chemical reaction and the energy out of a chemical reaction? They must be equal! LAW OF CONSERVATION OF ENERGY!
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A dog with a mass of 3000 kg sits at the top of a 5 m hill. If the dog has 150 kJ of potential energy, what is the potential energy halfway down the hill? New PE = initial PE 2 New PE = 150 kJ 2 New PE = 75 kJ
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What happens to the sum of potential and kinetic energy as the skater moves on the track? Stays the same Law of conservation of energy!
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At what point is the potential energy the greatest? The least? A B C D E Greatest: A Least: B A
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Which point(s) have less kinetic energy than point C? A & E A B C D E
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If 500 J of work is put into a system and 330 J is released as light, how much was “lost” to friction? 500 J – 330 J = 170 J
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Normally, which type of wave travels slowest? Sound
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If a wave travels at 331 m/s and has a frequency of 6.5 Hz, what is the wavelength? λ = V f λ = 331 m/s 6.5 Hz λ = 50.9 m
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A wave with a frequency of 2 Hz and a wavelength of 5000 nm is traveling at what speed? V = λ x f V = (5000 nm) x (2 Hz) V = 10,000 nm/s
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Define refraction. When a wave moves into a different medium, changes speed, and bends
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What are two differences between destructive and constructive interference? Destructive- overlap of crest/trough; causes decrease in amplitude Constructive- overlap of 2 same things; causes increase in amplitude Waves must be traveling toward each other!
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What type of wave is shown below? What’s an everyday example of this type of wave? Transverse light A B C
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A B C Which letter represents the amplitude of the wave? B
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Which letter represents the wavelength of the wave? A A B C
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If the wave travels in 4 sec, what is the frequency? f = cycles t f = 2 cycles 4 s f = 0.5 Hz A B C
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If the pitch of the sound gets lower, what happened to the wave? The frequency decreased
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If you turn up the volume on your stereo, what happened to the wave? The amplitude increased
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When a sound wave moves from air into the wall, what happened to the speed of the wave? It increased
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Which wave shown below is a sound wave? What is the name of this type of wave? the top one Longitudinal (compression, pressure)
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Complete the statement: Waves carry _____, not _____ from one place to another. (hint: fishing bobber) Waves carry ENERGY not MATTER from one place to another
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What makes something echo? Reflection of sound wave
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Define reflection When wave hits a surface and bounces back
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What type of electromagnetic wave has the greatest amount of energy? Gamma
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What type of electromagnetic wave has the longest wavelength? Radio
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What color has the lowest frequency? Red
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Thunder is heard _____ lightning strikes because____________. Thunder is heard AFTER lightning strikes because sound travels slower than light.
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Which electromagnetic waves are mostly responsible for skin cancer, sunburn, and cataracts? Ultraviolet
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Why are RADIO messages delayed when we send a message to astronauts on the moon? GREAT distance
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What type of wave is emitted (given off) by the sun? Ultraviolet
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Define current Charges flowing thru a circuit
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Define resistance Opposes (goes against) the flow of electrons
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Can a neutral object be attracted to a positive object? If so, how? If not, why? (Hint: think balloon and wall) Yes- the charges in the neutral objects can be rearranged
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When you rub a balloon on your hair, what’s happening with the charges? Electrons (negative) are moving from hair to balloon, causing balloon to have an excess charge (too much)
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What are two differences between a parallel and series circuit? Parallel- more than one option for e- travel, one bulb out doesn’t ruin the entire circuit (looks like a ladder) Series- only one path for e- travel, one bulb out means all out (one big circle)
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If you double the charge of one object, what happens to the force between them? Increases by 2 –2 x 1
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If you cut the charges of both objects by ½, what happens to the force between them? Decreases to ¼ (½ x ½) Decreases by 4
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If you cut the distance between two objects to ¼, what happens to the force between them? Increases by 16 –(¼) 2 = 1/16, then inverse!
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If you double the distance between two objects, what happens to the force between them? Decrease by 4 Decrease to ¼ –2 2 = 4, Inverse!
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