Ncert Exercises & Solutions

A wooden block with a coin placed on its top, floats in water as shown in the figure.

The distances \(l\) and \(h\) are shown in the figure. After some time, the coin falls
into the water. Then,

(a)	\(l\) decreases
(b)	\(h\) decreases
(c)	\(l\) increases
(d)	\(h \) increases

Choose the correct alterative/s:

1.	(b), (c)
2.	(a), (d)
3.	(c), (d)
4.	(a), (b)

Hint: The upthrust depends on the volume of the water displaced.

Explanation: When the coin falls into the water, the weight of the (block + coin) system decreases, which was balanced by the upthrust force earlier. As the weight of the system decreases, the upthrust force will also decrease, which is only possible when \(l\) decreases. As \(l\) decreases, the volume of water displaced by the block decreases, thus \(h\) also decreases.
Therefore both \(l\) and \(h\) decreases.
Hence, option (4) is the correct answer.

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