<h2>i also posted the question in SAT subject test section </h2>
<p>i try to figure it out, but cannot. someone help plz</p>
<p>answer is D, but why??</p>
<p>based on the equation U = - GMm/r, when objects are released, as the r decrease, G, M, m are constants. U approaches 0.................</p>
<p>based on the equation U = - GMm/r, when objects are released, as the r decrease, G, M, m are constants. U approaches 0.................</p>
<p>That is TRUE if your x-axis was r, unfortunately, it's in terms of time...</p>
<p>at t=0, U=0 because you are at r = infinity but as the object moves closer to the larger mass, the U gets more and more negative.</p>
<p>OK I am only in AP Physics B, but I think I may know why. This could be completely wrong but....</p>
<p>They are at infinity at start... they are attracted and get closer together, which decreases r. When r is decreased the magnitude of U is increased. I think you just have it wrong thinking that when r decreases, U must decrease too, but it's the opposite because its an inverse.</p>
<p>edit: Earth-dragon got it covered =P</p>
<p>k got it thx XD</p>
<p>i become kinda dumb after all these tests................man.........
cannot really focus............</p>
<p>it's D and it's.....right!!!! yay!</p>
