Okay this is Tom from every step physics dot com we’re gonna work an actual physics problem here problem number 8 on my sheet which I’ll shall show you and let’s do it get to my menu you know it’s a collision or momentum problem..ah because the words and so you know scroll down here to collision
and this decide which from other words in the problem with what they’re talking about in this case number eight they’re talking about a head-on collision so we’re gonna choose 2 which is collides and we’re going to do head on which is 7 I show you the formula for the final velocity of mass 1 and mass 2 final velocity this is the actual formula you can see CR here whic is the coefficient of restitution that’s the bounce ability of a substance and sometimes they give you that to enter into the problem or not and if they do then you’re in good shape here but they find this out by experimentation and the lists of substances about what they’re coefficient of restitution is for instance a super ball which is the most bouncy thing on earth is .78 coefficient of restitution doesn’t come up to one because if it came up to one that would mean that if you drop it from a hundred feet it would bounce right back up in your hand which gravity won’t let it do it so there is no possibility of one clay as an example the coefficient of restitution of zero and that defines whether it’s a perfect elastic collision if it has a coefficient of one or a perfectly inelastic collision which is sticking to mass is sticking and not bouncing off at all so let’s continue here um here’s a note here, if an object is at rest that’s the m2 mass to enter here so we have to press alpha first gonna press alpha and put in the mass that’s not at rest which is 10 you choose kilograms that’s what it says the second mass alpha twenty also kilograms initial velocity is coming at it at what does it say 3 meters per second we choose number three here and it’s going in the easterly direction or the plus X axis direction choose that and we have the initial velocity of the the mass 2 which is at rest if its at rest we enter 0 Alpha 0 and coefficient of restitution if it’s not given just enter one alpha 1 I show you what you’ve entered you can change it if you want looks pretty good to me were going to say okay and I give you both final velocities of both because they’re both gonna bounce off somewhat go somewhere and so the velocity final velocity mass 1 was minus point one notices its going off to the left there with the minus sign after they hit and here’s the final velocity mass 2 and 2 is positive so it’s going off to the right two meters per second so that’s the calculations notice on the test they do have plus 2 is meters per second and so you circle that one and get a hundred percent on it pretty neat huh..every step physics dot com and because you know its a collision problem our momentum problem you’re going to scroll down to a collision if you didn’t know it was that
Hello this is Tom for every step physics dot com I’m gonna do actual test problem number seven on the sheet here which I’ll show you the problem and let’s get started you go to my main menu and because you know it’s a collision problem our momentum problem you’re going to scroll down to a collision
if you didn’t know it was that you and you thought it was momentum you would go to momentum and it’d take you to the same spot but and this one here decides certain words in a problem to see whether it’s a momentum problem or a collision problem in this case number seven says is what releases scroll down to that thing that separates momentum problems from collision problems that the two masses are at rest at the beginning so they can’t collide so just a little information there
and we’re gonna find the bullets final velocities so we’re join to choose final velocity of mass 2 we’re gonna enter mass 1 which is you have to press Alpha before you enter anything in my programs Alpha 120 and it says gram so we’re gonna choose grams a show you how to convert that put that on your paper and
the bullets mass is 5 grams does a quick conversion and the releasing velocity is alpha .5 meters per second and because we’re releasing or pushing you have to you push off to the left if you were it was happening in reality and you push to the right so our velocity is gonna go to the left which is number two
becomes a minus and I check and see if tell you show you so that you can see if you’ve entered the right stuff or if you are happy with it I say it’s okay and momentum is p1 is the momentum of mass one which is the gun and the puck an that’s the mass times the velocity so it’s minus .06 kilograms per meters per second and because one of the rules in physics P one plus p2 equals zero we have the p1 is minus .06 so that becomes a a positive number for p2 because they’re equal and then we can figure the final velocity
of the bullet which is 12 meters per second pretty neat huh, every step physics dot com