Mhmm okay thanks, so if the rope had a mass, the two people would exert a force to make sure the rope didn't fall.. But now what about this (still can't solve a tension problem); a 2.00-kg textbook rests on a frictionless, horizontal surface. A cord attached to the book passes over a pulley whose diameter is 0.150m to a hanging book with mass 3.00 kg. The system is released from rest, and the books are observed to move 1.20m in 0.800s. (a) What is the tension in each part of the cord? My attempt; before the system is released from rest, the tension equals 3.00 x 9.81 = 29.4 N. This is because the rope is in equilibrium and no forces act except at its ends, so the tension is the same at both ends and throughout the rope. (Right?) But I don't understand what to do after the system starts moving. There is only one force acting, so the tension should be 3.00 x 2.00 x 9.81 = 58.9 N, but the answer is 7.5 N, 18.2 N.