7.17 A meter stick is balanced on a knife edge at its centre. When two coins, each of mass 5 g are put one on top of the other at the 12.0 cm mark, the stick is found to be balanced at 45.0 cm. What is the mass of the meter stick?

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Vishal Baghel | Contributor-Level 10

4 months ago

Mass of the meter stick = W

Mass of each coin = 5 g

When the coins are placed 12 cm away from the end P, the centre of mass gets shifted by 5 cm from point R towards the end P. The centre of mass is located at a distance of 45 cm from point P.

The net torque will be conserved for rotational equilibrium about point R,

10 x (45-12) – W' (50-45) = 0

W' = (10 x 33)/5 = 66 g

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