1. The problem statement, all variables and given/known data An assembly line has a staple gun that rolls to the left at 1.0 m/s while parts to be stapled roll past it to the right at 3.0 m/s. The staple gun fires 10 staples per second. How far apart are the staples in the finished part? 2. Relevant equations r = r' + Vt 3. The attempt at a solution I set the frames of reference to be the staple gun (S) and the part to be stapled (S'), assuming that their origins coincide at t = 0. The coordinate system will be right = positive. I think that the object is also the part to be stapled. The velocity of the staple gun relative to the part will be -4.0m/s while the velocity of the part relative to the staple gun will be 4.0 m/s. (Do I need any formulas for that?) The position of the part is then given by: r = r' + Vt Since I assumed that the origins coincided at t = 0, then position is: r = Vt So then substituting the velocity and assuming 1 sec has elapsed: r = (4.0m/s)(1.0s) r = 4.0 m Since the staple gun fires 10 staples/sec, the distance between the staples should be 4.0 m/ 10 staples/sec, but that gives me 0.40 m*sec / staple. Am I doing something wrong?