Q.A slingshot has two strings, each making an angle of $30^\circ$ with the line of action of the applied pulling force $F=50\text{ N}$, as shown in the figure. Apply Lami's theorem and calculate the tension in each string.

Step 1. The slingshot has two strings, symmetric about the direction of the applied force F=50 N, each making angle θ=30° with the line of action of F (mirroring the baby-swing example, but with an applied force replacing gravity).

Step 2. By symmetry, both strings carry the same tension T, and their components perpendicular to F cancel by symmetry, while their components along the (opposite) direction of F together balance F. …

Use the symmetric two-string equilibrium relation T = F/(2cosθ), exactly as derived for the swing example in this unit, with …

• Using sinθ instead of cosθ (the angle here is measured from the line of F, so the balancing component uses cosine). …