Here is a link to the image: http://img500.imageshack.us/img500/2681/171812nv.gif [Broken]

I found the initial momentum to be [itex]\left(50\cos{30^o},-50\sin{30^o}\right)[/itex] and the final momentum to be [itex]\left(50\cos{25^o},50\sin{25^o}\right)[/itex]. To find the change, I just subtracted these, but the answer is incorrect. Note: The method I used to find the initial and final vectors was to multiply the magnitude of the velocity by sine and cosine respectively, and then by 2 (the mass).

Can someone give me a hint as to where I went wrong?

Thank you.

Last edited by a moderator: Apr 21, 2017 at 9:17 PM

Now you know the horizontal and verticial components of the impulse, but you need to add the vectors together to find the total impulse. Drawing these 2 vectors will form a right triangle in which you can use pythagorean theorem to find the total impulse.

I don't have an answer for it, but it does give me a hint. It says that the impulse delivered to the mass by the plate only has a y-component. Does this mean I can get rid of my x component and use the y? For this problem, does that hint mean I would use (0,46.1) instead of (2.01,46.1)?

Hmm, that's strange. If ∆px = 0, then px` = px but that clearly isn't the case here since the angle of incidence and the angle of deflection are not equal. I don't see how they can make that claim. I'm just as stumped as you are now. :yuck:

Hmm... I found the answer, which is the one I suggested above (0,46.1). I find that strange as well, but I guess I'll just have to work with some similar problems.

Oh okay, I see the problem we both made here. We assumed that the final velocity of the ball was equal to the inital velocity but the question didn't state that. Tricky...