An odd world. Midterm 2 review. Mid term on Thursday. Conservation of energy

Transcription

1 Midterm review Day 15: Any final questions about nukes? Review Reminders: No HW this week! An odd world You find yourself in some diabolical plot where you are given an alpha (a) source, beta (b) source, and gamma (g) source. You must eat one, put one in your pocket and hold one in your hand. You a) a hand, b pocket, g eat b) b hand, g pocket, a eat c) g hand, a pocket, b eat d) b hand, a pocket, g eat e) a hand, g pocket, b eat Radioactive materials and radiation Daughters often have too few neutrons to stick together, so radioactive, divide more. Other bad/energetic stuff Neutrons helium nuclei ( alpha pa electrons ( beta particles photons ( gamma rays ) Mid term on Thursday - Balcony areas will be CLOSED on Thursday ~30 multiple choice questions Total 40 points. -There will be no early or late exams given and no make-up exams unless we have already discussed it. - Exam will be closed book. - TWO 3 by 5 inch formula cards. You can WRITE anything on it BY HAND. Please write your student ID on your formula card. -Calculator and pencil/eraser - Calculator cannot connect to outside world. No calculators on cell phones or laptops allowed. - No sharing of calculators. - A limited supply of spare calculators are available (no guarantees they work though!) - Exam grades and solutions will be posted after the exam on DL. Midterm preparation Prepare by: review the review notes for day 15! reviewing all the lecture notes (day 9-14), hw (4-6), and then book apply the principles we have learned -- practice (HW, clicker questions etc.) study with others come to the help room There are sample problems for you to review in addition to today. See web. Prepare by applying the principles we have learned practice. You CANNOT memorize answers to specific questions. Make a formula card now with the important equations. Go over homeworks, class clicker questions, questions in the book (see 1010 website - Not sure how to get the answer take it to the helproom. Conservation of energy - Work done by a force = F d // - Looked at work done by external forces and by friction - GPE = mgh, KE = ½ mv, PPE = PV, SPE= ½ kx, Thermal energy = constant T - Ramps, roller coasters, balls. - Power = energy/s Bernoulli s equation Midterm summary W ext - W friction = DPE + DKE - Conservation of energy for an incompressible fluid Conservation of energy I m moving boxes into the back of a truck that sits 1.4m above the ground. I use a 15m long ramp and a small cart to help me. When loaded, the cart has a mass of 0 kg. Friction is negligible. What is the direction of the net force on the cart, when it is on the ramp and nobody is pushing it? A Nuclear Energy - potential energy wells of nucleus -Alpha decay -Fision & Fusion -Radioactivity 1

2 If the cart has a mass of, how much PE does it gain when you push a J b. 196 J c. 8 J d J e J If the cart has a mass of, how much PE does it gain when you push a J b. 196 J c. 8 J d J e J GPE = mgh = 0 kg ( 9.8 m/s ) 1.4m What is the force required to lift the cart vertically at a steady speed? a. 0 N b. 8 N c. 300 N d. 196 N What is the force required to lift the cart vertically at a steady speed? a. 0 N b. 8 N c. 300 N d. 196 N F lift mg Steady speed a = 0 a = 0 F net = 0 F net = F lift mg F lift = mg = = 196 N What is the force required to push the cart up the ramp at a steady spee a. 196 N b N c. 0 N d N What is the force required to push the cart up the ramp at a steady spee a. 196 N b N c. 0 N d N W ext - W fric = DGPE + DKE F ext d = mgh F ext = mgh/d = 74.4 / 15 = 18.3 N

3 What length of ramp would I need if I could only push at a maximum force of 1 N? a m b m c..9 m d. 8. m What length of ramp would I need if I could only push at a maximum force of 1 N? a m F b m ext d = mgh d = mgh / F c..9 m ext = 74.4 / 1 =.9 m d. 8. m A cart is at the top of the ramp and I accidently let it go. It rolls down the ramp and then into thick grass on a horizontal lawn. The lawn rubs on the cart and produces a force of friction of 80N. How far across the lawn does the cart travel before coming to a stop? a..3 m b. 6.9 m c. 4.4 m d. 3.4 m A cart is at the top of the ramp and I accidently let it go. It rolls down the ramp and then into thick grass on a horizontal lawn. The lawn rubs on the cart and produces a force of friction of 80N. How far across the lawn does the cart travel before coming to a stop? GPE KE Thermal (= work done by friction) GPE = W friction = F friction d d = mgh/f friction = 74.4/80 = 3.4 m a..3 m b. 6.9 m c. 4.4 m d. 3.4 m up the ramp. Friction is now significant and is 50N. What is the total work that I do pushing a box to the top of the ramp at a steady speed a. 750 J b J c J d J up the ramp. Friction is now significant and is 50N. What is the total work that I do pushing a box to the top of the ramp at a steady speed W ext - W fric = DGPE + DKE a. 750 J b J c J d J W ext = DGPE + W fric = mgh + F fric d = J = J 3

4 up the ramp. Friction is now significant and is 50N. Work to push one box up ramp = J. If I have an average mechanical power output of 60W, how many boxes do I slide up the ramp in one hour? a. 10 b. 4 c. 17 d. 43 e. 170 up the ramp. Friction is now significant and is 50N. Work to push one box up ramp = J. If I have an average mechanical power output of 60W, how many boxes do I slide up the ramp in one hour? a. 10 b. 4 c. 17 d. 43 e. 170 Work done in one hour = 60 * 60 * 60 = J Number of boxes = J/104.4 J per box = 10 Water distribution in skyscrapers E tpv = GPE here The skyscraper water problem: Less pressure on the higher floors, Water won t make it to the top floor. How can you solve this problem? Put very high pressure pump at bottom (give water enough PPE at bottom) Use a series of pumps up the building Pump water to a tank on the roof, then you will always have pressure on the floors below. I m designing a fountain for a city park. I want the water in the fountain to squirt vertically in the air. What pressure will I need in the large pipe just before the nozzle? (Assume that friction can be ignored) a Pa b. 80 Pa c. 80,000 Pa d Pa e. More information required I m designing a fountain for a city park. I want the water in the fountain to squirt vertically in the air. What pressure will I need in the large pipe just before the nozzle? (Assume that friction can be ignored) a Pa b. 80 Pa c. 80,000 Pa d Pa e. More information required Top of water jet: v = 0, P = 0, h = In pipe: v = 0, h = 0, P =? E tpv is same in both locations P pipe = rgh jet = 1000*10*8 = 80,000 Pa What is the speed of the water immediately after the nozzle? a. ~15.3 m/s b. ~1.5 m/s c. ~8.7 m/s d. ~ 4.3 m.s e. Water does not come out 4

5 What is the speed of the water immediately after the nozzle? a. ~15.3 m/s b. ~1.5 m/s c. ~8.7 m/s d. ~ 4.3 m.s e. Water does not come out Inside pipe: v = 0, P = 80,000 Pa, h = After nozzle: v =?, h = 0, P = 0 E tpv is same in both locations P pipe = ½ r v v = sqrt (P pipe /r) = sqrt ( * 80,000 / 1,000 ) = 1.6 m/s If the fountain squirts m 3 of water in the air every second, what is the power produced by the pump that is supplying the pressurized water to the nozzle? a W b. W c W d. 37,806 W e. 156,800 W tunneling difficulty = width x depth of tunnel If the fountain squirts m 3 of water in the air every second, what is the power produced by the pump that is supplying the pressurized water to the nozzle? a W b. W c W d. 37,806 W e. 156,800 W Power = energy supplied to water / sec = GPE gained by water /sec = mgh/s = (m/s) g h Mass of water squirted per second = m kg/m 3 = 000kg in every second Power = 000kg/s 9./s 8 m = 156,800 kg m /s per second = 156,800 W E nucleus1 3 How much energy released? a. 1 most, second, 3 least b. most, 1, 3 least c. 3 most,, 1 least d. 3 most, 1, least energy is difference from bottom of crater to outside. 3 is most, second, 1 is least 8 tunneling difficulty = width x depth of tunnel E nucleus1 3 Rank these from decays (nucleon s escape) fastest to slowest. a. 1 fastest, second, 3 slowest The barrier is smallest in 3 so it b. fastest, 1, 3 slowest is fastest. c. 3 fastest,, 1 slowest 3 is fastest, second, 1 is d. 3 fastest, 1, slowest slowest 9 In atomic bomb, roughly 0% of Pl or Ur decays by induced fission This means that after explosion there are a. about 0% fewer atomic nuclei than before with correspondingly fewer total neutrons and protons, b. 0% fewer at. nucl. but about same total neut. and protons. c. about same total neutrons and protons and more atomic nuclei, d. almost no atomic nuclei left, just whole bunch of isolated Neut.s and prot.s., e. almost nothing of Ur or Pl left, all went into energy. ans. c. Makes and spreads around lots of weird radioactive daughter nuclei (iodine etc.) that can be absorbed by people and plants and decay slowly giving off damaging radiation. Lots of free neutrons directly from explosion can also induce radioactivity in some other nuclei. 30 5