Physics 103 Hour Exam #1 One Hour, Take Home, Closed Book

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1 Physics 103 Hour Exam #1 One Hour, Take Home, Closed Book Read these instructions carefully before beginning the exam. This exam is given under the Bryn Mawr honor code. Take it in a single sitting lasting no more than one hour. This is a closed-book exam: do not use any references (text, notes, etc.). You will need a calculator capable of basic functions (arithmetic, logarithms, trigonometric functions, etc.), but you are not allowed to store formulas, etc., in the calculator memory, and if the calculator has built-in unit conversion functions, you are not allowed to use them. You may use a computer if it acts only as a calculator to do basic arithmetic. Return your exam in class on Wednesday, September 26. Do not discuss this exam with anyone until all the exams have been turned in. When you begin the exam, remove the first sheet from the exam booklet. Write your answers directly on the exam booklet. Show your work and box your final answers. Partial credit is important! Always show your work! I can t give you credit if I don t know what you re thinking. In multi-part questions, if you get stuck on an early part, try to answer the later parts anyway either make up some answer for the early parts to use in the later parts, or describe what approach you would use to solve the later parts. If you need extra space to work a problem, use the back of another page of the test booklet. As announced in class, the exam book includes a small number of equations (not a comprehensive list), along with all physical constants that you need. Please do not assume that you will have to use all of the equations that are given, or that you will need to use every piece of information given in each problem. Sometimes in life you have more information than you need. Good luck!!

2 Physics 103 Hour Exam #1 Name Return this exam in class on Wednesday, September 26. Grading note: Each part of each problem is worth 5 points, for a total of 70 points. Equations: K = 1 2 mv2 U = mgh p = mv P V = n m RT Constants: g = 9.8 m s 2 R = J K 1 mole = ρ water = 1 g kg = 1000 cm3 m 3 1. The Earth is m from the Sun. The intensity of sunlight received at the Earth is 1300 W/m 2. If the Earth were twice as far away from the Sun, what intensity of sunlight would it receive? 1

3 2. A 10.0 m 3 chamber holding Nitrogen gas (N 2 ) is kept at a pressure of N/m 2 and temperature 300 K. The atomic mass of Nitrogen is (a) How many moles of N 2 gas does it hold? (b) What is the mass of gas in the chamber? (c) What is the number density of gas in the chamber? (d) If you heated the gas to 900 K while increasing the volume of the chamber to 20.0 m 3, what would the pressure be? 2

4 3. Imagine two fictitious elements, X, and Y, which combine via this gaseous reaction: 3X 2 + 4Y 2X 3 Y 2 Notice that X 2 is diatomic while Y is monatomic. The atomic masses of X and Y are 50 u and 75 u respectively. If you want to produce 1 liter of X 3 Y 2, how many liters of X 2 do you need, and how many liters of Y do you need? Assume that all the gases, both before and after the reaction, are at the same pressure and the same temperature. 3

5 4. The Hoover Dam is located on the Colorado River. The head of the dam is about 170 m high. This means that if water spilled over the dam, it would fall 170 m. The flow rate of water at the location of the dam is about acre-ft/year. One acre-ft equals 1230 m 3. There are seconds in one year. (a) How many cubic meters of water flow through the dam in one second? (b) What is the mass of water which flows through the dam in one second? (The density of water is 1000 kg/m 3.) (c) If that amount of water fell from a height of 170 m down to 0 m, what would its kinetic energy be at the end of the fall? (d) Assume all the kinetic energy is converted to electric power by turbines at the base of the dam. If water flows continuously, how much power can be produced, in Watts? (e) Average electricity consumption in the U.S. is about 1200 Watts per person. (This is split fairly evenly between residential, commercial, and industrial uses.) What population could be supported by the Hoover Dam? 4

6 5. Near the surface of Mars, the air pressure is 800 N/m 2. The gravitational acceleration is g = 3.73 m/s 2. How high a column of mercury could be supported by a barometer on Mars? The density of Mercury is 13.6 g/cm 3 or kgm How does the pressure in the Earth s atmosphere depend on altitude (height above the ground)? Give a qualitative answer: as you go up in altitude, does the pressure increase, stay the same, or decrease? Or can you not predict it? Justify your answer using physical principles. (A simple one-word answer will not get credit.) 5

Physics 121 Hour Exam #1 60 Minutes, Take Home, Closed Book

Physics 121 Hour Exam #1 60 Minutes, Take Home, Closed Book This exam is given under the Bryn Mawr honor code. Take it in a single sitting lasting no more than one hour. This is a closed-book exam: do