ratatat Posted April 29, 2009 Report Share Posted April 29, 2009 Hey guys, can anyone tell me why practice test 3R Question 77 has the answer as 200J ie. why you dont take into account the angle when doing the work calculation? http://i44.tinypic.com/m9myao.jpg ^^Link to the question. Thanks. Evidently, I will have to work on my physics skills. Link to comment Share on other sites More sharing options...
AdamP Posted April 29, 2009 Report Share Posted April 29, 2009 Lol don't quote me on this, because I don't know much. anyways remember first that work is a scalar quantity, that doesn't mean much in this case it seems like a bit of a trick question with them giving you all that trig info. Anyways if you think about the pully the entire force (both the x and y components) gets translated in to a vertical force on the mass (think about the FBD)so F (50N) * D (4M) = 200 J works another way to think about it that is probably a lot easier is the change in potential energy (J) which is also equiv. to the work done on the system, since the mass moves up 4 m U=mgh = 200J hopefully that helps a bit... Link to comment Share on other sites More sharing options...
rmorelan Posted April 29, 2009 Report Share Posted April 29, 2009 Lol don't quote me on this, because I don't know much. anyways remember first that work is a scalar quantity, that doesn't mean much in this case it seems like a bit of a trick question with them giving you all that trig info. Anyways if you think about the pully the entire force (both the x and y components) gets translated in to a vertical force on the mass (think about the FBD)so F (50N) * D (4M) = 200 J works another way to think about it that is probably a lot easier is the change in potential energy (J) which is also equiv. to the work done on the system, since the mass moves up 4 m U=mgh = 200J hopefully that helps a bit... AdamP is perfectly correct! Work is scalar, and equal to the change in potential energy of the mass in this case. As AdamP says that would be mgh. I love physics Link to comment Share on other sites More sharing options...
smile Posted April 30, 2009 Report Share Posted April 30, 2009 Pulley = machine Machines make our lives easier by reducing FORCE. A smaller person can push an object since less force is required with a machine. That being said, it's give-and-take with machines. When force is decreased, the force has to be exerted for a greater DISTANCE. In the instance of an inclined plane, an object must be moved a greater distance to get to a certain vertical height. Smaller force and greater distance = same total WORK. Remember, work = (Force)(distance). You can simply ignore the picture and answer the question based on the first sentence. Work will be the same no matter what machine (or lack thereof) is used. Link to comment Share on other sites More sharing options...
ratatat Posted April 30, 2009 Author Report Share Posted April 30, 2009 Thanks for the explanation guys. Link to comment Share on other sites More sharing options...
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