Two opposite forces F1 = 120 N and F2 = 80 N act on an elastic plank of modulus of elasticity Y = 2 x 10^11 N/m2. and length l = 1 m placed over a smooth horizontal surface. The cross-sectional area of the plank is S = 0.5 m2. The change in the length of the plank is x *10-11m Find the value of x. I understood most of the solution but I didn't get one part of it, which says: Tension at any point x in the plank T(x)= F2 + ((F1 - F2)/l)*x Why do we include the term F2? Shouldn't T(x) without the term F2 be the tension at the point?