Chapter 8 - Application of Trigonometry - Summary Exercises on Applications of Trigonometry and Vectors - Exercises - Page 792: 5

$42\ lb$

1. Draw a diagram as shown, assume the horizontal force is $F$, the tension of the rope is $T$ and $\theta=40^\circ$ 2. The gravity is $50\ lb$, for the force to be balanced, we have $T\ cos40^\circ=50$ and $F=T\ sin40^\circ$ 3. Combine the two equations, we have $F=50 tan40^\circ\approx42\ lb$