A small 42.0 N sign is suspended from the end of a hinged rod, which is 2.40 m long and uniform in shape. (Fig

Question

A small 42.0 N sign is suspended from the end of a hinged rod, which is 2.40 m long and uniform in shape. (Figure 1.35) What tension force exists in the rope holding up both the rod and the sign? The rope makes an angle of 60° with the 36.0 N rod.

Image:http://img155.imageshack.us/img155/5812/equi4qb4.png

Answer: 69N

Answer 1

As unknown forces exist at the pivot, take moments about that point to eliminate them:

36 * 1.2 + 42 * 2.4 = F sin(60) * 2.4

F = (36 * 1.2 + 42 * 2.4) / (2.4 sin(60))

= 69 N.