We can’t do much more with the x -component of momentum, so now let’s look at the y -component.
(Note the negative sign on Maggie’s y -velocity!)
Okay. Now we have two equations and two unknowns. It’ll take some algebra to solve this one, but none
of it is too hard. We will assume that you can do the math on your own, but we will gladly provide you
with the answer:
The algebra is not particularly important here. Get the conceptual physics down—in a two-dimensional
collision, you must treat each direction separately. If you do so, you will receive virtually full credit on an
AP problem. If you combine vertical and horizontal momentum into a single conservation equation, you
will probably not receive any credit at all.
Practice Problems
Multiple Choice:
First two questions: A ball of mass M is caught by someone wearing a baseball glove. The ball is in
contact with the glove for a time t ; the initial velocity of the ball (just before the catcher touches it) is v (^0)
.
1 . If the time of the ball’s collision with the glove is doubled, what happens to the force necessary to
catch the ball?
(A) It doesn’t change.
(B) It is cut in half.
(C) It is cut to one-fourth of the original force.
(D) It quadruples.
(E) It doubles.
2 . If the time of collision remains t , but the initial velocity is doubled, what happens to the force
necessary to catch the ball?
(A) It doesn’t change.
(B) It is cut in half.
(C) It is cut to one-fourth of the original force.