Find the tension ( stretching force) on the string whie system is accelerating. I know that the pull on block "A" for acceleration is gm2 / m1 + m2. so what is the source of the kinetic energy store in block "A".
The key thing to understand is that this is a conservation of energy problem. Whatever PE the system loses will equal the KE that the system gains. Also realize that the system has two parts: block A and block B. Even though only one block actually falls, both blocks share the KE since they are attached.Bama said:Doc, here is what I have. This problem seems simple but nerving as well. Here is the question and choices I am given. What you say makes a lot of sense however the choices I have are hard for me to understand. Question: What is the source of the kinetic energy stored in block A? Now I know it isn't number one but the others are a bit confusing for me. It seems as if it's a play on words but if it isn't, what key element should I have notice?
The blocks gain KE, so this one doesn't make sense.1) In falling, block B loss kinetic energy that transfers to block A.
Block A moves horizontally so its PE doesn't change, so this one doesn't make sense.2) As it moves to the right, block A loses potential energy that transfers to kinetic energy.
OK, partly right: The PE of block B is reduced since B is the block that falls. But if all of the PE loss went into the KE of block A, then block B wouldn't move! So this answer can't be right. (The blocks share the KE.)3) The PE assiociated with the block B is reduced as block B falls and all of the PE loss is transferred to block A as KE.
That's the only one that makes sense.4) The PE assiociated with the block B is reduced as block B falls,but only part of this loss of PE is transferred to block A as KE.
In your diagram, block A moving to the right is moving horizontally. So left-right is just another way of saying horizontal. What's wrong with answer 2 is that it states "block A loses potential energy": that's not true. If something only moves horizontally, its gravitational PE does not change.Bama said:So with number 2 moving to the right should have never been consider because there isn't no left or right only horizontal and vertical.