On a frictionless air hockey table, puck A of mass 0.250 kg mo...

Question

On a frictionless air hockey table, puck A of mass 0.250 kg moves to the right and collides with puck B of mass 0.38kg, which is initially at rest. After the collision, puck A is moving the left at 0.12 m/s and puck B moves to the right at 0.65 m/s. What was the initial velocity of puck A before the collision?

Accepted Answer

Hey guys, hopefully got a chance to try this one on your own. We have to, hockey pucks that are going to collide with each other. So the first thing we want to do is we want to draw diagrams for before and afterwards. So here's what's happening. So I've got this hockey puck, I'm gonna call this one a 0.25 it's moving to the right and it's going to crash into another hockey puck, which I'm going to call B, which is initially at rest. So, you know, this initial velocity here is equal to zero. So that's the before and afterwards we know the final velocities of both of the pucks. So afterwards, what happens is we have puck a that's actually moving to the left now. So I'm gonna call this V. A. Final and we know that this is going to be left at 0 12. So this is gonna be 0 12 because it's left, it's going to pick up a negative sign. So basically what I'm doing, I'm gonna assume that the positive direction is my direction of positive throughout the whole problem. So we want to do is we want to figure out what's the initial velocity of this puck a. So finally we know that puck B is moving to the right, so this one is moving to the right at 0. m/s. That's my VB final here. So basically now I got three of the velocities. So I've got this one, this one and this one I'm gonna go ahead and stick the second step now and write my conservation of momentum equation. So this is M one V one initial plus M two V two initial equals M one V one final plus M two V two file. Alright, so I've got 0.25, we're gonna write the masses plus 0. Equals 0.25 plus 0.38. Just gonna write all the numbers. Then we'll figure figure out what goes inside the parentheses here. So the initial velocity of this 0.25 kg puck puck is actually the one I'm looking for. So this is my unknown variable via initial. So the rest, I actually know this initial velocity of puck B is actually equal to zero. That's what goes inside here and it goes away. And then finally we have negative zero points 12 for this guy, right? That's your. And then 0.38 is going to be 0.65. So you really just gonna plug and chug everything on the left and right sides. So you're gonna get zero points 25 via initial equals. And then on the right side which you get Is you should get 0.217 0.217. Now, you just divide by the 0.25 and you get a visa initial of zero 087 m/s. That's how fast puck it was going. So this is basically 0.87 in order for to collide the stationary objects. And then basically it's gonna ricochet back and they're both gonna be moving in opposite directions. All right. So that's that's really all there is to it guys, let me know if you have any questions and that's it for this one.

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