Question

an body acted upon by three forces f1, f2 and f3 is under equilibrium .given |f1|= 10n |f2|= 10n

Answer 1

Hello friend....!!!
Since force is a vector quantity it is added and subtracted though vector algebra.

In the question f1 f2 and f3 are the forces acting on the object but still the object is at equilibrium. So the three forces must balance each other, that is the net force acting on the object is 0.

In vector, if the resultant of 3 forces is 0 then their sum is also 0
So f1+f2+f3=0
10+10+f3=0
f3= –20

The magnitude of f3 is 20N and direction is opposite to f1 and f2

HOPE IT HELPS.... :-)