Question

A wooden block, with a coin placed on its top, floats in water as shown in the figure. The distance $l$ and $h$ are shown. After some time, the coin falls into the water. Then,

• A. $l$ decreases and $h$ increases
• B. $l$ increases and $h$ decreases
• C. Both $l$ and $h$ increase
• D. Both $l$ and $h$ decrease

Answer 1

The correct option is D Both $l$ and $h$ decrease

When the coin slips into the water, the wooden block moves up and $l$ decreases.
[because weight of water displaced by block alone is lesser than weight of water displaced by block + coin]

When the coin was floating, it displaced water equal to its own weight. When the coin is inside the water, it displaces water equal to its own volume. As its density is greater than that of water, it displaced more water in the first case.
Hence, $h$ decreases when it falls into the water.