PHYS 201     TEST #4         11/23/16         DR. HOLMES NAME 

Do all eight problems. The worth of each problem is marked beside the space for the answer. All answers should be in MKS units unless otherwise indicated. Show your work for partial credit. Work should be under the problem, or clearly labeled on an extra sheet placed underneath the top page of the test.

1)  a)  If you apply a force of 15 lbs on a cylinder of area 0.20 in2, what is the gauge pressure on the fluid behind the cylinder?

  in lb/in2:  75 lb/in2;    in Nt/m2: 5.15 x 105 Nt/m2 .

b)  If the fluid under the above pressure pushes on another cylinder of area 18 in2, what will be the force on this cylinder?

 in lbs:  1,350 lb.   in Nt:  6,014 Nt.

 

2) a) What is the gauge pressure at a depth of 900 feet (275 m) under water:?

in Nt/m²: 2.70 x 106 Nt/m2   in lb/in²: 392 lb/in2               in atmospheres:  26.7 atm.

 b) If you have a view plate on a submersible that is 900 feet below the surface (and subject to the gauge pressure in problem 2a above), what is the force due to this pressure on the view plate if the area of the view plate is 500 cm2 (circular plate of diameter 10 inches)?

In Nt:  135,000 Nt

In lbs: 30,300 lb.

 

3) A small artery of inside DIAMETER 0.62 mm and length 2.5 cm carries blood. Assume the beginning and the end of the artery are at the same height.

a) If the pressure drop from the front to the back of the artery is 4 mm Hg, what is the pressure drop expressed in Nt/m2 ?

532 Nt/m2

b) Assuming there is the above pressure drop, and given that the viscosity of the blood is 4 x 10-3 Pl (about four times that of water), what is the volume flow of blood per time through the artery (assume laminar flow) expressed:

in m3/sec: 1.93 x 10-8 m3/sec

in cc/sec: 0.0193 cc/sec

c) Given that the density of blood is 1.05 gm/cc, by how much would the blood pressure decrease due to gravity by going up a distance of 32 cm (from the heart to the head)?

In Nt/m2: 3,293 Nt/m2

In mm of Hg: 24.8 mm of Hg.

 

For problems 4 & 5, consider a house 46 ft x 30 ft x 8 ft with 1380 ft2 of floor (and ceiling) space and an outside wall area of 1,216 ft2 (46’ x 8’ plus 30’ x 8’ plus 46’ x 8’ plus 30’ x 8’).

4)  Assume the outside walls have thermal insulation due to sheetrock and fiberglass with a total value of R = 15 ft2*oF*hr/BTU.  Assume the average inside temperature is 68oF and the average outside temperature is 23oF.  Ignore other sources of heat loss such as through the ceiling, through the floor, via convection and radiation.

a)  What is the average heat loss per time (in Watts) due to conduction through the outside walls?

1,040 Watts

b) If the cost of energy is $0.095 / kW*hr, what will the cost be for a month to replace the energy lost by conduction?

$71.12

 c)  If the inside temperature is reset to 77o, what will the new average heat loss per time (in Watts) due to conduction through the outside walls be?

1,248 Watts.

 

5)  For the house above (46’ x 30’ x 8’):

a) What is the volume of air space in this room?

in ft3 :  11,040 ft3;      in m3 : 312.6 m3

Now assume the temperature in the room is set to be 77oF.

b) Calculate the number of moles of air in this house:

12,765 moles

c) Is the number of moles of air in the house when the temperature is 23oF [more, the same, or less] than when the temperature is 77oF ?

more.

d) Given that the heat capacity of air (at constant pressure) is (7/2)*R, how much energy would it take to heat up the air in this house from 23°F to 77°F ?

1.11 x 107 Joules = 3.09 kW-hr

e) At $.095 / kW-hr, what would this energy cost?

$0.294 = 29.4 cents

f) If the air in this house is replace by outside air at the rate of once every 3 hours, how much would it cost to keep this house heated for one month assuming the outside temperature and inside temperature remained constant during the whole month and assuming the outgoing hot air did not warm up the incoming cold air?  (Neglect other sources of heat such as warm bodies and losses due to radiation and conduction).

$70.46

 

6 a) How much energy does it take to heat up 475 cc's of water (16 fluid ounces)  (1 cc = 1 milliliter = 1 gram) from 77oF to boiling (212oF) ?

149,126 Joules = 35,625 calories

b) How much energy does it take to boil 475 cc's of water (if the water is already at 212oF) ?

1,073,700 Joules = 256,500 calories

c) If a person burns energy at the rate of 115 Watts, how much water (at 77o) is needed each hour to keep the person cool by evaporation (assume no heat is lost by conduction or radiation ?

161 cc/hr.

 

7) Assume a certain person has an average skin temperature of 92°F and a skin area of 0.84 m2.

a) How much energy does this person radiate per second (in Watts)?

419 Watts

b) If the air temperature is 41°F, how much heat energy per time does this person receive from the air due to radiation?

284 Watts

c) What is the net power lost or gained by radiation by the person?

135 Watts lost.

  

8)  a)  State the First Law of Thermodynamics:

 b)  Where does this law come from, that is, is it a re-statement of a previous law?

 c)  State the Second Law of Thermodynamics

 d)  Where does this law come from?:

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