00:01
So for this question, all we require is effectively a diagram of what's happening.
00:08
So this is before.
00:11
Draw a dotted line around.
00:14
Well, not very clear.
00:17
And this is after.
00:23
So we see before we have our particle, our alpha particle, which is marked in red, coming into some velocity v -i alpha.
00:32
And it's so i'll just mark this with alpha and this is our oxygen particle which i mark with o and then afterwards and o is at rest of the beginning and afterwards we get our alpha particle scattering at 64 degrees to the horizontal upwards with some velocity v final alpha and we also have our oxygen um oxygen atom scattering downwards 51 degrees to the horizontal at some speed vfnall which is given so vfo which is given in the question as 1 .2 0 times 10 to the 5 meters second so to get the components of these we're only going to really need the vertical components and you'll see why so the vertical component here is one point is the vf nor vfo multiplied by the sign of 51 and here it's vf alpha times by the sign of 64.
01:35
So we get our two velocities and the reason why we want the y velocities is we require that the momentum before is equal to momentum afterwards but this also counts in the various directions so the momentum in y before is meant to be is equal to the momentum in why after why don't we use x well in the advantage of the y is in the before state, if we used x, we'd have this another unknown, v, i, alpha, which we have no idea what it is, it doesn't give it into the question...
