Forces F1 and F2 act on the weightless lever. Find F1 if it is known that the shoulder of this force is l1 = 5 cm, F2 = 10 N and l2 = 2 cm.

According to the lever balance rule:
F1 / F2 = l2 / l1, where F1 is the force acting on the l1 shoulder; F2 – force acting on the shoulder l2 (F2 = 10 N); l1, l2 – lever arms (l1 = 5 cm, l2 = 2 cm).
Let us express and calculate the force F1:
F1 = (F2 * l2) / l1 = (10 * 2) / 5 = 20/4 = 4 N.
Answer: Force F1 is 4 N.