A meter stick balances at the 50.0-cm mark.If a 50.0-g object is placed at the 90.0-cm mark,the stick balances at the 61.3-cm mark.What is the mass of the meter stick?

Question

Quizplus · Accepted Answer

We can use the principle of moments, which states that the sum of the clockwise moments equals the sum of the counterclockwise moments. 
Let's call the mass of the meter stick M. When the stick balances at the 50.0-cm mark, the counterclockwise moment is zero. When the 50.0-g object is placed at the 90.0-cm mark, the counterclockwise moment is (50.0 g) * (40.0 cm) = 2000 g*cm. 
To find the clockwise moment, we can use the fact that the stick balances when the object is at the 61.3-cm mark: 
(M) * (50.0 cm) = (50.0 g) * (61.3 cm - 50.0 cm) = 565 g*cm 
Simplifying this equation, we get M = (565 g*cm) / (50.0 cm) = 11.3 g + 100 g =  127 g. 
Therefore, the mass of the meter stick is 127 g, which corresponds to choice (A).

A Meter Stick Balances at the 50