1. The problem statement, all variables and given/known data Consider the popgun in the figure below. The launching mechanism consists of a trigger-released spring. The spring is compressed to a position yA, and the trigger is fired. The projectile of mass m rises to a position yC above the position at which it leaves the spring, indicated in the figure as position yB = 0. Consider a firing of the gun for which m = 38.0 g, yA = -0.140 m, and yC = 22.0 m. Suppose, however, there is a friction force of magnitude 1.90 N acting on the projectile as it rubs against the interior of the barrel. The vertical length from point to the end of the barrel is 0.620 m. (Hint: you may need to calculate the spring constant from the information given.) (a) After the spring is compressed and the popgun fired, to what height does the projectile rise above point ? http://www.webassign.net/serpse8/8-figure-06-alt.gif Picture 2. Relevant equations Book gave this for no friction to solve for K K(c)+Ug(c)+Us(c)=K(A)+Ug(A)+Us(A) 0 + mgy(c) + 0 = 0 + mgy(a) + 1/2kx^2 k=2mg(y(c)-y(a))/x^2 3. The attempt at a solution I am confused how to use the above with friction involed. It's saying at Point C, KE = 0? Wouldn't that mean it reached it's maximum height ? (Assume this is wrong, would be to easy then) Do I do : Change in KE + Change in PE - Ffr* D for the length of the gun to find the velocity it leaves barrel and then use the velocity find how high that one goes ?