EXAM III -- PART A -- FLUIDS and THERMODYNAMICS

All work on this exam must be your own. You may use a calculator and a 3"X5" card of equations. Clearly indicate your final answer for each question. You are required to do ALL of the multiple choice problems and 4 of the 5 long-answer problems.

 

Section 1: Multiple choice. No partial credit will be given for this section. Circle only one answer for each question.

 

 1) The total random kinetic energy of the atoms or molecules in an ideal gas is equal to

a) the temperature of the gas.

b) the internal energy of the gas.

c) the heat of the gas.

d) both b) and c) are correct.

 

2) When you hold an ice cube in your hand, heat flows from your hand to the ice via

a) conduction.

b) convection.

c) radiation.

d) None of the above.

 

3) Which of the following is true of the second law of thermodynamics?

a) It states that the entropy of an isolated system cannot decrease. b) It implies that heat will flow spontaneously from a colder object to a warmer object.

c) It can be derived from the principle of conservation of energy.

d) None of the above.

4) In a pool open to the atmosphere, the absolute pressure is measured to be P1 at a depth of h1. At twice that depth (at a depth 2h1) the absolute pressure would be measured to be

a) 2P1.

b) P1/2.

c) 4P1.

d) none of the above.

 

 

5) "The velocity of the fluid at each point remains constant in time" is a definition of

a) compressibility.

b) viscosity.

c) steady flow.

d) tube of flow.

 

 

6) Choose the answer which correctly fills the blanks. The continuity equation can be derived from ____, and Bernoulli's equation can be derived from _____.

a) the first law of thermodynamics, the second law of thermodynamics.

b) conservation of matter, conservation of energy.

c) the first law of thermodynamics, conservation of energy.

d) conservation of momentum, the second law of thermodynamics.

 

 

7) The direction of the buoyant force acting on an object is a) Always up.

b) Always down.

c) Up for an object which floats, and down for an object which sinks.

d) None of the above.

8) If the length of a solid rod increases by 1% when heated, then the temperature change of the rod is a) 1%.

b) more than 1%.

c) less than 1%.

d) dependent on the type of material the rod is made of.

 

 

9) Below P-V diagrams representing the cycles of various engines. Which engine does the most work in one cycle?

 

 

 

 

a) engine A.

b) engine B.

c) engine C.

d) engine D.

 

 

10) If you hold your hand horizontally in the air, the forces due to air pressure will be exerted

a) downward, on the top of your hand.

b) downward, over the entire surface of your hand.

c)  upward, over the entire surface of your hand.

d)  over the entire surface of your hand, everywhere normal (perpendicular) to the surface.

 

 

The following tables copied from the textbook may be helpful to you in solving problems in section 2. (specific heats, heats of transformation, thermal conductivities)

 

Section 2: Problems and questions. Choose four of the following five problems. Do all sections of each problem you choose. If you attempt more than four problems, please indicate which four you wish to have graded.

Partial credit will be given for this section. Show ALL WORK and JUSTIFY all answers. Be sure your answers include UNITS where appropriate.

11) An ideal gas expands at a constant pressure of 1X105 N/m2 from a volume of 5 m3 to a volume of 6 m3. a) Find the work done by the gas.

b) If the initial temperature of the gas is 50oC, find the final temperature of the gas.

c) Find the change in internal energy of the gas.

d) Find the heat absorbed in the process.

12) 50g of liquid silver at a temperature of 963oC is solidified and cooled to a temperature of 900oC.


a) What is the entropy change for the silver during the solidifying part of the process?

b) What is the total entropy change for the silver during the entire process?

c) Does your answer to part (b) indicate a violation of the second law of thermodynamics? Why or why not?

 

13) A cube-shaped container, 20 cm on a side, is filled to the top with liquid. The total mass of the liquid is 6kg. Assume the top of the liquid is open to the atmosphere. a) What is the density of the liquid?

b)Find the force exerted on the bottom of the container by the liquid.

c) If a styrofoam ball of mass 10g and density 200kg/m3 is placed in the liquid, will it float or sink? Why?

d) How much liquid will spill when the ball is placed in it?

 

14) Water flows through a pipe.  At point A the radius of the pipe is 10 cm, the pressure is 8X105 N/m2, and the rate of flow is 0.03 m3/s. Point B, where the radius is 8 cm, is 10m higher than point A.

 

a) What is the rate of flow at point B?

b) What is the speed of the water flowing past point B?

c) What is the water pressure at point B?

d) Using the fluid dynamic principles we learned this term, describe the source of the "lift" force acting on an airplane wing. Recall that the cross-section of the wing looks like this: