Question

The figure shows a beaker containing mercury. If a rectangular iron bar of mass 850 g is dropped in the mercury contained in this beaker, what will be the apparent weight of the iron bar?

• A. Equal to the weight of the displaced liquid
• B. Less than the weight of the body (non-zero)
• C. Zero
• D. Can’t be determined

Answer 1

The correct option is C

Zero

The density of iron bar is less than the density of mercury, thus the iron bar will float inside the beaker containing mercury. According to the principle of floatation, when a body floats in a liquid, the weight of the body is balanced by the up thrust on it, which is equal to the weight of liquid displaced by its submerged part. Thus, the up thrust on the body by the liquid is equal to the weight of the body. Hence, a floating body appears to have no weight (or its apparent weight is zero).