Question

A boy who weighs 800 N and his 475 N little sister are 3.5 meters apart from each other on a balanced see-

saw.

a) What is the mass of the little sister?

b) How far away is the little sister sitting from the center of the see-saw?

Answer 1

a) The mass is

$$m=W/g=475/9.8=48.5\text{ kg}.$$

b) By equilibrium of moments:

$$800·(3.5-x)=475x→x=2.2\text{ m}.$$