Please explain attachment image problem

Since, it is given the mass of string as well as block, and they are under motion by a common force F, then they would posses common acceleration, because no any obstructing force acts on them. In the same way by drawing the FBD(where reactional force is considered), we can find the tension in the string. 2. a. In the first case, we just assume the string as whole mass system, then it would have acceleration a = F/m b. If we want to find the tension at any position in the string, we need to assume a small mass element 'dm'. Now, we will put all the force equation on this mass element, Fnet = 'dm' a Here, tension force at that point in the string would be responsible formotion. 3. In vertical case, as string carries mass, so tension force which a function of weight, will vary from bottom point to top most point, because mass is given for string. Consider a mass element, calculate its weight, tension at that point would be the remaining hanging part... Then applu the Newton;s eqns... Good Luck..........................