Question

the greatest and the least resultant of twoforces acting on a particle are the 35KN and 5 KN respectively. if 25KN is the magnitude of the resultant for the given system of forces f1 and f2 .prove that the forces are acting at right angle

Answer 1

a+b = 35
a-b = 5
so
a = 20
b = 15

c^2 = a^2+b^2 - 2 a b cos C
625 = 400 + 225 - 2 a b cos C
so cos C = 0
C = 90 or 270 degrees