Teaching Physics with the Physics Suite

Edward F. Redish

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The meteor and the dolphin

The curator of a science museum is transporting a chunk of meteor iron (i.e., a piece of iron that fell from the sky see picture at left) from one part of the museum to another. Since the chunk of iron weighs 250 pounds and is too big for her to lift by herself, she is using a handtruck (see figure at right).While passing through the marine mammals section of the museum, she accidentally hits a bump and the meteorite tips off the handtruck and into the dolphin pool. Fortunately, the iron didn't hit a dolphin, but it quickly sinks to the bottom. "Rats!" she cries. Unfortunately, the meteorite has many sharp edges and she is worried the dolphins, curious creatures that they are, will come to inspect it and be cut when they rub against it. She wants to get it up out of the pool as quickly as possible. Fortunately, the meteorite has lots of holes in it and there are ropes with hooks on one end lying around. If she could get a hook into one of the holes, she might be able to pull it up to the top, tie the rope around a post, and lever it out with the handtruck. Unfortunately, she remembers that the meteorite is too heavy for her to lift.

(a) Will the fact that the meteorite is in the pool under water make it harder or easier for her to lift with the rope? Explain.

(b) The meteorite is sitting on the concrete bottom of the pool. Is the force the meteorite exerts on the bottom bigger or smaller than the force it would exert if the pool had no water in it? Explain.

(c) Can she lift the meteorite? Calculate how much force she would have to exert on a rope hooked to the meteorite to pull it up from the bottom of the pool. She can lift about 100 pounds, the pool is 12 feet deep, and the density of iron is about 8000 kg/m3.

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Page last modified October 10, 2002: M07