# Selina Solutions Class 9 Physics Solutions for Exercise 5C in Chapter 5 - Chapter 5 Upthrust In Fluids Archimedes Principle And Floatation

Question 13 Exercise 5C

A block of wood is so loaded that it just floats in the water at room temperature. What change will occur in the state of floatation, if

(a) Some salt is added to water,

(b) Water is heated

(a) It floats with some part outside water.

The density of water increases when salt is added to water, so the upthrust on the block of wood increases, and therefore, the block rises up till the weight of salty water displaced by the submerged part of the block becomes equal to the weight of the block.

(b) It sinks.

The density of water decreases on heating, hence the upthrust on the block decreases, and the weight of the block exceeds the upthrust as a result of which it sinks

Video transcript
hello everyone welcome to leto this is priyan and here we have a question about density and flotation let us look into the question a block of wood is so loaded that it just floats in the water at room temperature what will change what change will occur in the state of flotation if some salt is added to the water in this case when some salt is added to the water it floats this wood floats with some part outside the body the for the wood will floats with some part outsider outside the water this is because the density of water increases when salt is added to the water the water density water density increases with the increase of salt content so salt is added the water density increases so the up thrust on the wood increases and therefore the block rises up till the weight of the salt water displaced by the submerged part of this wooden block which becomes equal to the weight of the block when this water is added with the sand the salt the water density increases and this makes the up thrust a thrust of the block of the wood to increase up thrust of the wood also increases because of this the block rises up till how much salt water has displaced how much salt is displaced depending on that this level the block rises up okay and this block will rises up till the weight of the flow of the block is equal to the submerged part of the block hope you understand also we have one more question when water is heated so in the first case when water is added with salt what happens so when water is added that the wooden block starts to float with some part outside the water but when it is heated so when the water is heated it starts to sink the wood sinks because the density of water here the density of water decreases with the increase in temperature so when when we are heating more and more and giving more temperature to the water the water density decreases and the uprest on the wooden block also decreases because of this at rest on the then block also decreases with the decrease in density of water wooden block also decreases and the weight of the block exceeds the uprest as a result in the sink sinking of this wooden block into the water so when the density of water decreases it makes the uprest on the wooden block also decreases and this makes the weight of the block exceeding the upthrust as a result the block will sink hope you understand this video if you like my video please subscribe to our little channel and if you have any doubts you can keep a message in comment box thank you
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