Two more dive physics problems

[Jim Lapenta]

Agreed, I don't see any value in just giving him the answer. But from some of the replies it's obvious we have people here with actual salvage experience who can explain how to figure it as well as things that the books do not cover adequately such as safety factors and real world practices. Sometimes showing that from a practical standpoint the book is full of crap with the answers they offer for choices.

Since I started reading this thread an idea has been forming for my own classes - get rid of multiple choice answers wherever possible. Use essay questions that require the student to actually think about how, why, when, where, etc.. With the goal being to stop encouraging them to look for a one or two word answer in the text and answer the question in their own words. Same with fill in the blanks. I see a number of test questions that don't really require anyone to do more than memorize a sentence. Sometimes without even thinking about the context or what it actually means to a diver.

I am on Rev 4 of the exam for my HOG reg tech course. The first one that I received as an instructor was really bad. I've had to remove obvious PR stuff, reword questions that were set up for absolute answers when that was simply not the case, and put some in that require the student to go through the manual and search for the answer.

I can see doing this with my AOW, UW Nav, and other courses to bring them up to the next level and provide the student with an incentive to learn the material rather than just memorize it.

 

[Rich Keller]

Low for the student or low for the people who are supposed to be teaching? Why not:

1. An object is a five ft. [-]square and five ft. high[/-] cube and is floating in the ocean. Six inches of the object is above the waterline. What is the [-]minimum line strength that would be needed to lift the object out of the water[/-] gross weight of the object? (Of course you would need to include the correct value.)

2. [-]If a diver takes a sealed, rigid, cubical container measuring 10 inches per side to a depth of 20 ft. in the ocean, the total crushing force (assume the wall thickness is zero) on the container would be about:[/-] What is the total hydrostatic force acting on a hallow sealed 10" cube with one atmosphere inside at an average depth of 20 FSW (Feet of Sea Water)?

The total force is different if the maximum or minimum depth is 20'. The average depth compensates for the 5" above and below the average. The wall thickness is irrelevant because you are only interested in the external surface area and the differential pressure.

I would also rewrite the lift bag question from the other thread. Why not start with the 150lb object on the boat, tie the person who came up with these questions to the object and then drop it over the side? That solves all three problems at once right?