Three horizontal ropes pull on a large stone stuck in the ground, producing the vector forces shown in Fig. P1.60. Find the magnitude and direction of a fourth force on the stone that will make the vector sum of the four forces zero.

Answer : Step 1: Three horizontal ropes pull on a large stone stuck in the ground , producing the vector forces A , B and C shown in the fig below, Now finding the magnitude of a fourth force on the stone that will make the vector sum four forces Step 2: Now the X- component 0 0 0 Rx= 100cos30 + 80cos120 + 40cos233 + Dx = 0 Dx= -22.53N Step 3: the Y- component Ry = 100sin30 + 80sin120 + 40sin233 + Dy = 0 Dy = -87.34 N