A meter stick balances horizontally on a knife-edge at the 50.0 cm mark. With two 5.12 g coins stacked over the 24.2 cm mark, the stick is found to balance at the 27.8 cm mark. What is the mass of the meter stick

The mass of the meter stick is  

Explanation:

Here since the meter stick is in equilibrium position its net torque and net force should be equal to zero

      Since at the begging the meter stick is balanced at center of the meter stick that means its center of mass should be present at

Now lets consider the later case where stick is balanced by two 5.12 g coins .

Here torque due to two coins =

  Torque due to weight of meter stick =   =  

  where m = mass of the meter stick

    Here .

Upon equating we will be getting mass of the meter stick =

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.