HewittDrewit PHYSICS 26 FishLunch Momentum Problem

here's an inelastic collision problem that begs for a solution by way of momentum conservation a 5 kilogram fish swims at 1 meter per second toward and swallows a smaller one kilogram fish at rest find the velocity of the larger fish immediately after lunch ignore the effects of water resistance since there's no outside forces acting on the two fish system we know that the net momentum before lunch will be equal to the net momentum after lunch following the physics the initial momentum of the large fish is 5 kilograms times 1 meter per second add this to the initial momentum of the small fish which is zero after lunch the net momentum is the combined mass times V what we're looking for continuing and cancelling kilograms we see that the velocity after lunch is 5/6 meters per second this velocity is in the same direction as the initial velocity of the large fish we employ the conservation of momentum and come to a solution YUM suppose the small fish is not at rest but swims toward the left at four meters per second find the velocity of the larger fish immediately after lunch again ignore the effects of water resistance as before the net momentum before lunch equals the net momentum after lunch we have the initial momentum of the large fish plus the initial momentum of the fish with velocity equal to minus four meters per second and after lunch we have the combined mass times the velocity V that we're looking for so we see the initial momentum is five kilograms meters per second minus four kilograms meters per second in negative direction relative to the large fish which equals six kilograms times V you combining terms and cancelling kilograms we find V equals one six meters per second what happens here is the negative momentum of the small fish effectively slows the large fish after lunch you suppose the smaller fish was swimming twice as fast at eight meters per second then we make use of a prior calculations changing minus four meters per second to minus eight meters per second you here we see the final velocity is minus 1/2 meter per second what's the significance of the minus sign after lunch the two fish system moves backward toward the left yom-yom physics at least according to the large fish I want to leave you with a question how fast with the small fish have to swim before lunch to halt the large fish in its tracks that is what speed brings the net momentum to zero until next time good energy

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