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A rifle is fired and you are able to measure both the muzzle velocity of the bullet as well as the recoil velocity of rifle how do you explain the fact that the forward velocity of the bullet is great?


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August 18, 2008 5:45PM

The force exerted on the bullet and the recoil force against the rifleman, are equal to each other (for every action there is an equal and opposite reaction). The bullet has a very small mass, and the rifle/rifleman possess a large mass, force is equal to one half mass times velocity squared, F=m/2*v^2. So velocity of the bullet is the square root of twice force divided by mass, small mass equals large velocity. Another way of looking at this problem is to invoke the law of the conservation of momentum: mass(bullet)*muzzle_velocity(bullet) = mass(rifle)*recoil_velocity(rifle). This is an approximation that neglects the momentum carried away the propellant (both spent and unburned) that exits the muzzle after the bullet.