1. The problem statement, all variables and given/known data A projectile enters a resisting medium at x=0 with an initial velocity v0=900ft/s and travels 4in before coming to rest. Assuming that the velocity of the projectile is defined by the relation v=v0-kx, where v is expressed in ft/s and x is in feet, determine (a) the initial acceleration of the projectile, (b) the time required for the projectile to penetrate 3.9in into the resisting medium. Answers: (a) -2.43x106ft/s2 (b) 1.366x10-3s 2. Relevant equations xi=0ft vi=900ft/s xf=4in=.33333ft v=vi-kx vf=0ft/s (rest) a(x)=d/dx[v(x)] 3. The attempt at a solution v=vi-kx 0=900-k*.33333 ----> k=2700s-1 a(x)=d/dx[v(x)]=d/dx[vi-kx]=-k=-2700 The answer of -2.43x106ft/s2 is obviously not -2700.