Q1:

A pin-jointed tower truss is loaded as shown in the given figure. The force induced in the member DF is

ANS:A - 1.5 kN (tension)

1.5 Tension.

The reaction at F will be 4.5 upward.
And taking vertical equilibrium we have;
3/5 FC - FD = 4.5.

Now, the force in FC will be compressive only and subtracting force FD is equal to reaction 4.5 which means force FD and reaction is in same direction i.e upward which means the force FD is a Tension force