Two objects are connected with a string. In the quantitative treatment of the problem we assume that the string exerts a tension force of magnitude T on each of the two objects. What do we need to assume for this assumption to be valid?

Question

a) the string may hang loose between the objects
b) the string does not pass over a pulley
c) the string is massless
d) the two objects are not on a collision course with each other
e) none of the above