Question

You have a bag of cotton and an iron bar, each indicating a mass of $100kg$ when measured on a weighing machine. In reality:

• A. cotton is heavier than iron
• B. cotton and iron are equally heavy
• C. iron is heavier than cotton
• D. none of the above

Answer 1

The correct option is A

cotton is heavier than iron

Explanation for correct option:

1. The correct answer is the cotton bag is heavier than an iron bar. The bag of cotton is heavier than the bar of iron.
2. The cotton bag experiences a larger air thrust than the iron bar. Therefore, the weighing machine indicates less weight than its actual weight for the cotton bag.
3. Because, True weight = (apparent weight + up thrust)
4. The cotton bag’s density is less than that of the iron bar, so the volume of the cotton bag is more compared to the iron bar. So the cotton bag experience more upthrust due to the presence of air.
5. Therefore, in the presence of air, the cotton bag’s true weight is more compared to the true weight of the iron bar.

Hence, the correct answer is option (A) i.e. cotton is heavier than iron.