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Question 81.
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So we have three carts, mass of m, 2m, and 4m.
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The first two carts are moving with the same velocity, v -0.
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The third cart is at rest.
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These carts smash together and stick.
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We're supposed to find their final velocity and also compare their ratios of kinetic energy.
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So final velocity will start by using conservation and momentum.
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We have v -0 times m plus v -0 times 2m plus 0 because this one's at rest, has to equal their final velocity, v, times their total mass now, which is m plus 2m, plus 4m, which is 7m.
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We can combine these terms, v .0m plus v .0m is 3v0m, or 3m times v0 equals v .7m.
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There is an m on both sides.
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We'll get rid of that, and then we'll go ahead and divide by 7, divide by 7, and we'll see that 3 7th of v0 is our final velocity.
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So our final velocity is 3 7ths of v .0...