[shannah]

	Quote: Originally Posted by niccolo98
	Hey guys, I take a physics AP course. We wrote a test yesterday, and there was one question that did not seem right. The question was: A body with the mass of 3.6 kg gets dropped from a height of 30m. The body hits the floor at 20 meters per second. Calculate the mechanic energy that gets turned into heat energy DURING the fall, not the impact. To my understanding, at those speeds, the heat that is created due to friction is so little, that it barely has an effect on the loss of energy. So, thats what I wrote. He wrote a big fat wrong next to that. This is how he said it is calculated. E potential= m (mass) times g (gravitational pull. about 10) times h (height) If you put all those numbers in there, you get 1080N for the potential Energy. Do this for the kinetic energy aswell: E kinetic= m (mass) divided by 2 times v squared (speed squared) Put the numbers in, and get 720N. He then says, you subtract 720N from the 1080N. Get 360N. He says, that this then equals the energy that is converted to heat. That is one third of the total potential energy. I am almost certain, that at those speeds, not one third of the total energy gets converted to heat. I am also sure, that for one to calculate the heat created, that the frontal area of the object is needed. Again, something that is not given in the question. Please help me. I have been searching the internet for hours. One more question is, what factors acctually take (convert) energy in a falling object? The 360N might be right, but I dont think that all the energy gets converted to heat. Please help before I go insane looking through physic forums. Thanks in advance, Nick

Hi Nick,
This isn't an aerodynamics issue. It is just straight physics. All the energy gets converted to heat. Don't try to think of it in a real world or rational sense. Just do the math. The example you are working with isn't real world, so don't expect the answer to reflect anything that might be rationalized by observation or logic.