12/7/20101Students without registered clickersbinberaiemke4193hallljkksingermayfiejvrobo1755sich8052vubwestreicClickers without student names188CBC28CDD79A818C5904DCF8DF2B1BB1862C1D94EC651DA990241DDAA4631DE9E6121FB6D871E666D051FC5944EE9374E967CFF85F818A0498A24A7F8DFF7DA36AB97If you’re on either list, let me know!Announcements• Final exam: Next Monday, Dec. 13 • Location: here, the regular classroom, G1B30 .• Time: 4:30-6:30 PM. Contact me today if you will need extra time.• Format: Multiple choice, true/false• You can bring: • three 3X5 index cards with handwritten information (one from each midterm, one more for the final) • a calculator• a number 2 pencil• You cannot have: and open text book or other notes. • Coverage: comprehensiveHow to best study for exam?1. look at old homework, exams, and clicker questions andsee if you know answers (without looking at answer sheet).2. Explain to skeptical friend (and vice-versa).ElectrocutionRequires about 100 mA (0.1 A), but it has to have a path through your heart.Radio• Broadcast by currents going back and forth in antenna• Propagates as electromagnetic wavefor all EM radiation, c = 3 X108m/s• Received by driving currents back and forth in another antenna.cMicrowave ovens• Water molecules have a positive end and a negative end• Microwaves cause them to rotate, bang into each other, which heats liquid water.• Microwaves can’t “fit” through holes smaller than their wavelength.• Standing waves: microwave ovens have hot spots and cold spots.--+12/7/20102Discharge lamps and fluorescent lights• Atoms can only have certain energies.• When an electron “jumps” to a lower level, it gives off light as a photon, with energyE = hc/, where h = 6.6 x 10-34J s and c= 3 x 108m/s • Higher energy UV photons hurt you more than lower energy visible light. • Phosphors absorb UV photons, emit lower energy visible photons.We drop a superball from height of 10 m, sketch plot of velocity and acceleration and position vs time as ball falls, bounces, and rises back up close to starting position.+0-VelocitytimeAcceleration+0-time+0-positiontime100feetDropsuperballWe drop a superball from height of 10 m, sketch plot of velocity and acceleration and position vs time.+0-VelocitytimeAcceleration+0-time+0-position+0-VelocitytimeAcceleration+0-time+0-positiond. Same as A except position acceleration is always negative and constant.e. Same as C except acceleration is always negative and constant.ABtime+0-VelocitytimeAcceleration+0-time+0-positionCWe drop a superball from height of 10 m, sketch plot of velocity and acceleration and position vs time as ball falls, bounces, and rises back up close to starting position.100feetDropsuperballtime+0-VelocitytimeAcceleration+0-time+0-positionCVelocity: Starts at zero and becomes faster and faster in negative direction. At floor, large change in velocity, now fast and positive. Slows down as gravity exerts downward force on ball. Position: starts at positive 10 meters, goes slowly at first, speeds up as falls. Hits ground (0 meters) and then heads back up. Acceleration is constant and negative when force of gravity is only force acting on ball. When ball is in contact with floor, 2 forces act on ball … force of gravity and force of the floor on the ball. NET force is upwards at that point and acceleration is positive. Acceleration (a) = change in velocitytime elapsedAs a bicyclist passes you, he is traveling at 2 m/s uphill when he stops pedaling. His acceleration in the direction down the hill is now 1.5 m/s2, what will his velocity be 1 second later?a. 1.5 m/s up the hill b. 1.5 m/s down the hill c. 3.5 m/s down the hill d. 0.5 m/s up the hill e. 9.8 m/s down the hillIn eqns: Initially heading up the hill at 2 m/s, define up as positive direction: Final velocity = initial velocity + acceleration x timeFinal velocity = 2 m/s + (-1.5 m/s2) x (1 sec) = 0.5 m/sAnswer is d. 0.5 m/s up the hill. Acceleration of 1.5 m/s2 down the hill = (1.5 m/s) per second.Means that for each second, the bicyclists velocity will changeby 1.5 m/s tending towards heading down the hill. So if initially heading up at 2 m/s, now heading up only at 0.5 m/s (or 1.5 m/s slower than before). Change in velocityPer secondAfter 2 seconds? Velocity is 1 m/s down the hill. . You are building a water system for your house where you pump water out of a well up into a water tower in the back yard. If you want to make sure that the water pressure at the kitchen sink never drops below 250 kPa no matter how much water is in the water tower, how high above the sink must the bottom of the water tower be? (Choose the answer closest to the correct value.) a. 15 m; b. 20 m; c. 25 m; d. 30 m; e. 35 msolution:Step1 draw picture,figure out what is needed.distance?Step 2. Conceptual look: What is going on with energy of the water at different points in the system?12/7/20103. You are building a water system for your house where you pump water out of a well up into a water tower in the back yard. If you want to make sure that the water pressure at the kitchen sink never drops below 250 kPa no matter how much water is in the water tower, how high above the sink must the bottom of the water tower be? (Choose the answer closest to the correct value.) 15 m; b. 20 m; c. 25 m; d. 30 m; e. 35 mdistance?As water moves from water tower to kitchen sink, gravitation potential energy is converted into pressure energy. Energy here: lots of gravitational potential energy, little KElittle pressure energy (when take almost empty)Energy here: No GPE (define h=0 here)little KElots pressure energydistance?As water moves from water tower to kitchen sink, gravitation potential energy is converted into pressure energy. Energy here: No GPE (define this as h=0)little KElots pressure energy(Pressure + ½ r v2+ rgh )at tower=(Pressure + ½ r v2+ rgh )at sinkEnergy in water at tower = Energy in water at sink00PE + KE + GPE = PE + KE + GPEKE: Small and same as for pipe to sinkso cancel … distance?rgh )at tower =(Pressure )at sinkrg x distance )at tower =(Pressure )at sinkDistance = (Pressure )at sink/ rgDistance = 250,000 Pa/ (1000 kg/m3x 9.8 m/s2) = 25 mEnergy here: No GPE (define this as h=0)little KElots pressure energy(Pressure + ½ r v2+ rgh )at tower=(Pressure + ½ r v2+ rgh )at sinkEnergy in water at tower =