ICSE Class 9 Answered

a.Archemedes' principle: When a body is partly or wholly immersed in a fluid, it experiences an upthrust, which is equal to the weight of fluid displaced by the immersed part of the body.

b. 1. Take a cork and weigh it in the air by a physical balance.

    2. Take a sinker (a glass stopper) and weigh it in the water.

    3. Tie the sinker to the cork and weigh the combination under water.

Observations:

Wt of cork in air                                                      = W   ...............(i)

Wt of sinker in water                                              =   ............(ii)

Wt of cork in water + Wt of sinker in water             =  ............(iii)

Therefore, Wt of cork in air + Wt of sinker in water = W +  ........(iv)

Subtracting (iii) from (iv)

Wt of cork in air - Wt of cork in water = W + -

Therefore, R.D of cork =

                                  =