Hi everyone, this is my first post to the forums. Nice to meet you all and thank you in advance. 1. The problem statement, all variables and given/known data A bullet of mass 6.00g is fired horizontally into a wooden block of mass 1.21kg resting on a horizontal surface. The coefficient of kinetic friction between block and surface is 0.210. The bullet remains embedded in the block, which is observed to slide a distance 0.260m along the surface before stopping. What is the initial velocity of the bullet? Mass of bullet = 6.00g = 0.006kg Mass of block = 1.21kg (+bullet) = 1.216 Coeff. of friction µk = 0.210 ∆d = 0.260m 2. Relevant equations ∆KE + ∆PE = -Wnc KE = 1/2mv^2 Work = F∆d F(kf) = µk(N) *F∆t = m(vf - vi) 3. The attempt at a solution F(sf) = Coeff. friction x normal force = (.210)(1.21)(9.8) = 2.49 N Work = F∆d Work done by friction = (2.49N)(0.260m) = -0.647 J No potential energy here so... KEf - KEi = -0.647 KEf = 0 (the block slid to a stop) KEi = -0.647 1/2mvi^2 = -0.647 vi = √(2)(0.647)/0.006 = 14.64 m/s ...Which is incorrect. *Because this problem is in the chapter on momentum it seems like they want me to use an equation involving momentum, but I don't know 1)if this problem can or cannot be solved with the work-energy theorem and 2) when I would use the momentum equation in the above scenario. For the record I also tried finding the initial velocity of the block (1.03 m/s) and putting that as my KEf for the bullet but the difference was negligible. Any advice greatly appreciated - thank you!