Redneck Engineering Exam

    Most engineers are familiar with this "Redneck Engineering Exam".  It's been going around in email for several years now.  I decided to take a shot at it myself, so I chose four of the essay questions (there were no multiple choice questions so I assumed this was the afternoon session) and took a whack at them.  I can only hope I passed.

  1. Calculate the smallest limb diameter on a persimmon tree that will support a 10 pound possum.
      • Assumptions:  Location - Southern United States in a tree located well off main road (close proximity to highway dramatically increases the odds of possum falling out and rolling into traffic), Date – after Nov. 1 (After first “hard” frost, leaf and persimmon load at lowest level), Average Possum body weight = 0.75 Average Coon body weight
      • Solution: Trick question.  Coons, with much better eyesight and an equally accurate sense of smell, stripped every limb of persimmons after first frost.   Any remaining limbs will bear no persimmons, hence Possum will not climb tree.
  2. Which of the following cars will rust out the quickest when placed on blocks in your front yard? 66 Ford Fairlane, 69 Chevrolet Chevelle, 64 Pontiac GTO.
      • Assumptions: “Rusting out” refers to an un-drivable condition.  "Driving" would entail motorized transportation of eight family members to a relatives home on the opposite side of the family land.
      • Solution:  The 66 Ford Fairlane.  While the rear quarter panels of the 69 Chevrolet Chevelle will rust out within two weeks of “blocking”, the curved roofline will prevent most moisture from entering the passenger compartment. Total loss of the rear quarter panels will not render it un-drivable.  No 64 Pontiac GTO has ever been left up on blocks.  Ford’s history of window regulator mechanism failures during the 63-68 model years will not permit the side windows to remain in the closed condition after abandonment.  Within 6 weeks the entire floorboard and seat springs will be lost to rust and the seat will fall through.  In the unlikely event that the vehicle's engine has not "seized up" and can be jumped off, friction due to the wet seat binding on the driveshaft will engulf the vehicle interior in smoke within the first few yards of forward motion.
  3. If your uncle builds a still that operates at a capacity of 20 gallons of shine per hour, how many car radiators are necessary to condense the product?
  4.  A pulpwood cutter has a chain saw that operates at 2700 rpm.  The density of the pine trees in a plot to be harvested is 470 per acre. The plot is 2.3 acres in size.  The average tree diameter is 14 inches. How many Budweiser Tallboys will it take to cut the trees?
  5.  If every old refrigerator in the state vented a charge of R-12 simultaneously, what would be the decrease in the ozone layer?
  6. A front porch is constructed of 2x8 pine on 24-inch centers with a field rock foundation.  The span is 8 feet and the porch length is 16 feet.  The porch floor is 1 inch rough sawn pine.  When the porch collapses, how many hound dogs will be killed?
      • Assumptions:  Porch load includes three individuals (avg. 120 lbs. each), one wet, upholstered couch (420 lbs.) and one pick-up truck bench seat (132 lbs.).  Assume instantaneous, catastrophic failure of porch supports.  Overhead structure weight is approximately equal to porch structure weight.  Overhead structure contributes to initial loading but does not impart secondary impact load.  Assume hound dogs are symmetrically distributed under porch.  Clearance between dog (s) and porch is 1foot.  Average dog weight 45 lbs., average thickness (in supine or prostrate position) 12 inches and the average dog compressibility factor is assumed to be 0.4.
      • Solution:  The density of white pine (values for yellow pine aren’t available) 25 lbs per cubic foot.  With a porch area of 128-sq. ft., the total weight of the porch, occupants, furniture and overhead structure, is 1522.6 lbs.  Neglecting the resistance of air, the porch will be impart a force of Ws/d, where W = weight of porch and attachments, s = total distance porch falls and d = distance of dog compression.  Thus, F = Ws/d or 1522.6 lbs. * (8 ft. + 0.4 ft)/( 0.4 ft)   or 31975 lbs. equally distributed between dogs.  If the life/death threshold for the dogs is equal to dog weight/compressibility factor, 45 lbs/0.4 = 112.5 lbs. / dog.  Calculating the maximum “dead” dog load as (Ws/d)/X=112.5 lbs./dog where X represents the number of dogs or X=284.2 dogs.  Rounding to integer values 284 dogs could be killed and one slightly injured.  However, 285 dogs could not fit underneath porch, thus ALL dogs under the porch would, unfortunately, be killed.
  7. A man owns a Tennessee house and 3.7 acres of land in a hollow with an average slope of 15%.  The man has 5 children.  Can each of the children place a mobile home on the man's land?
      • Assumptions: Lot is basic rectangle of 1 x 2 proportion.  Local code enforcement is non-existent.  Homeowner has a single 8 square foot  “2-holer” outhouse, one cistern of approximately 10 square feet, a 1000 square foot garden plot, a 200 square foot pig parlor and 200’ x 8’ dirt driveway pre-existing.  The existing “Jim Walter” home covers approximately 900 square feet.  The homeowner provides his home and property as collateral in each purchase, thus ensuring minimum trailer house dimensions of 14’ x 80’. Family size will be per local standard
      • Solution:  Each 14’ x 80’ trailer has a footprint of 1136 square feet with trailer tongue and front cinder block steps included in footprint (per tradition, no back door steps are provided).  Each child will require 384 square feet area for obligatory salvage vehicles plus an additional 192 square feet for one operational vehicle (includes buffer zone for brake failure).  A common recreational area for family events will require 400 square feet.  The youngest child will require an additional 600 square feet for an automotive repair shop.  If the total property occupant load follows tradition and is maintained at 45 people, ( two grandparents and one in-law in the existing home and two parents, one in-law and five children in each of the trailers with an additional two children of undetermined lineage floating from trailer to trailer), no additional toilet facilities will be required (assuming the vertical capacity of the existing 2-holer can be increased).  This is also based on a usage rate of 20 minutes per person per day or 15 total hours.  The current cistern will supply sufficient water since daily usage is near zero.  At a 1 x 2 ratio, the length of 567.8 feet and a depth of 283.9 feet and an average slope of 15 degrees, the actual surface area of the lot is [567.8/ cos(15)] 283.9 = 166884.9 square feet or 3.8 acres.  The total area required will be 13278 square feet at a minimum indicating a surplus of 153606.9 square feet.  However if the next generation follows suit, and assuming no marriages of siblings, the occupant load could reach as many as 228 individuals.  The additional required multi-hole outhouse and 25 trailer house placement will be dependant on acquiring the adjoining acreage currently occupied by the appliance salvage yard.
  8. A 2-ton pulpwood truck is overloaded and proceeding 900 yards down a steep grade on a secondary road at 45 mph.  The brakes fail.  Given the average traffic loading of secondary roads, what are the chances that it will strike a vehicle that has a muffler?
  9. A coal mine operates a NFPA Class 1, Division 2 Hazardous Area. The mine employs 120 miners per shift.  A gas warning is issued at the beginning of 3rd shift.  How many cartons of unfiltered Camels will be smoked during the shift?
  10. At a reduction in gene pool variability rate of 7.5% per generation, how long will it take a town that has been bypassed by the interstate to breed a country-western singer?

    I feel pretty good about the ones I answered and I know if I had a little more time I could get a couple more.

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