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Momentum and Kinetic Energy in 1-Dimensional Explosions

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I'll be demonstrating some collisions to you In order to obtain some data that you'll be using in some calculations to investigate the conservation of momentum and kinetic energy. A particular kind of collision that we'll be looking at is an explosion. An explosion is a collision or interaction in which the objects are not moving with respect to each other to begin with. After the explosion, the objects are separated. Now we're doing a special kind of explosion, one that occurs in a straight line under controlled conditions, and we're using this track for that purpose. So we've got two carts which are the objects. That will explode away from each other on this track, this track is level, and there's very low friction between the carts and the surface of the track. So we've done that in order to minimize any possible influence of external forces. In order to produce the explosion, the carts, which by the way are as nearly identical as possible, have spring loaded plungers, and I can push one of the plungers in, and release that spring very quickly with a pin, and so I'll do that now. Now, we're going to need to be able to calculate momentum and kinetic energy and in order to do that we'll need the masses and velocities. The masses of the two carts are the same as I said before (mcart = 0.500 kg). We can put different amounts of mass on them to give them different masses. In order to get velocities, we need to time how long it takes the cart to pass a certain distance and we're using the photo gates for that purpose. Each cart will have a flag on it (Flag width = .050 m), the flag is just a post-it note, and when the flag passes through the photo gate, the photo gate will count. It only counts when the photo gate beam is blocked. And so if one takes the width of the flag and divide it by that amount of time, that would tell you the velocity of the cart. So let's do the first collision. For the first one, we're not putting any bars on it. Reset the photo gates. And the readings for the time are (ΔtL = 0.086 s) for the left cart, that's your left, and (ΔtR = 0.079 s) for the right cart. So those are very nearly the same as we might expect. For the next collision, I'll put one bar on the right cart, and since the mass of the bar and the cart are both half a kilogram, that means the right cart has twice the mass of the left cart. I'll reset the timers. And here it goes. And the time readings now are (ΔtL = 0.0700 s) for the left cart and (ΔtR = 0.149s) for the right cart. For the next collision, I'll add a bar to the left cart, so both carts have the same mass again, reset the timers and the time readings for the left cart (ΔtL = .128 s) and for the right cart (ΔtR = 0.119s). For the fourth collision I'll add a bar to the left cart and reset the timers. And the time readings are (ΔtL = 0.128 s) and ΔtR = 0.103 s) that does it for the collisions. Next you'll go to a webpage and do some calculations in order to see if momentum and kinetic energy are conserved in these collisions.

 



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