Adart is inserted into a spring-loaded dart gun by pushing the spring in by a distance x. for the next loading, the spring is compressed a distance 2x. how much faster does the second dart leave the gun compared to the first? the book gives an answer of "two times as much" but i not totally clear on what equation this is coming from. is it the equation: w(ext) = 1/2mvf^2 - 1/2mvi^2 where the initiial velocity would be 0?