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

When a floating coin falls in water the overall level of water in container will go down as earlier the coin was floating and displaced amount of water is equal to the weight of the coin where as when it falls in water displaced water is less than the weight hence l will decrease. As the total displaced water is due to the wooden block, after coin falls in the tank h will also decrease.