Question

A wooden block, with a coin placed on its top, floats in water as shown in figure. The distance $l$ and h are shown there. 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

Answer: (A)

l decreases and h increases

Answer 2

When the coin is on the block, the total weight supported by buoyancy is $(m_w + m_c)g$. The submerged depth $l$ is proportional to this total weight. When the coin sinks, the weight supported by buoyancy becomes $m_w g$. Since the weight decreases, the submerged depth of the block ($l$) decreases. As the total height of the block is constant ($h_w = l + h$), a decrease in $l$ leads to an increase in $h$.