#6Q1) Mechanics and Properties of Matter

Determination of the mass of a body using the principle of moments

DifficultyEasy
Est. Time45 mins

Required Apparatus

A metre ruler, a knife edge, a 50 g weight, a glass stopper or a small stone (of about 50 g mass), a piece of string, and a block of wood (3′′×4′′3^{\prime\prime}\times4^{\prime\prime}).

Scientific Theory

Image

In the position of equilibrium, according to the principle of moments,

m0g×y=mg×xm_{0}g\times y=mg\times x y=(mm0)xy=(\frac{m}{m_{0}})x

Gradient of the graph of y against x=mm0x = \frac{m}{m_{0}}

m=gradient×m0m = gradient\times m_{0}

Experimental Method

  1. Place the knife edge on the stand and on it balance the metre ruler horizontally.
  2. As shown in Figure 6.1 suspend the known mass m0m_{0} and the unknown mass mm on opposite sides of the knife edge and adjust length yy keeping length xx at a selected value until the ruler is balanced horizontally. Measure the values xx and yy.
  3. Repeat the experiment for five other selected values of xx so as to obtain a wide spread of readings.
  4. Enter the readings in the table. When taking readings take care to keep the balancing point of the ruler on the knife edge unchanged at the original position.

Important Points

1
  • Measure the mass of the body using a balance and calculate the percentage error of experimental value.
2
  • Explain with reasons of any deviations.