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

Question 39 Exercise 5A

A block of mass 3.5kg displaces 1000cm3 of water when fully immersed inside it. Calculate:

(i) the volume of the body, (ii) the upthrust on the body, and (iii) the apparent weight of the body in water.

Given:

Mass of block = 3.5kg => weight of the body = 3.5kgf

The volume of the water displaced when completely immersed in water = 1000cm3

(i) To find the volume of the body when completely immersed in a liquid is equivalent to the volume of the water displaced

Volume of the block = 1000 cm3 or 0.001m3

(ii) Upthrust acting on the body = volume of the body x density of water x g

= 0.001 x 1000 x g = 1 kgf

(iii) The apparent weight of body in water= true weight – upthrust

=3.5-1 = 2.5kgf

Video transcript
"hello everyone welcome to leader this is priya and here we have a question about to solve let us look into the question a block of mass 3.5 kgs displaces 1000 centimeter cube of water when fully immersed inside it calculate the volume of the body second the uptress on the body and third the apparent weight of the body in what so to find out the first one the volume of the of the body before that i'm just giving you the values what has given in the question it has given the mass of block which is 3.5 kgs that means we can also write the we can find the weight of this block by adding the force of gravity acting on it so weight of block will be 3.5 k g f the volume of the water displaced when completely immersed in in water is 1000 centimeter cube so the volume of water the volume of water displaced when completely immersed equal to 1000 centimeter cube and now to find out the volume of the body when completely immersed in the liquid will be equal to the volume of water displaced so then volume of the block what will be the volume of the block volume of the block volume of the block will be obviously 1000 centimeter cube or in meters we can express this as 0.000 one meter cube so this is the volume of block because the volume of block will be equal to the volume of water which is displaced when the block is fully immersed inside it so we have found out the first one now we'll see the second one which we have to find out the uprest on the body as we know aktrast acting on the body is equal to will be always equal to volume of the body into density of water and density of water and gravity we know the volume of the liquid which is zero point 0.001 meter cube and we know the density of water which is 1000 and we know the g we take it as a g which implies 1 k g f so up just acting on the body will be one kgf now we see the last one we have to find out the apparent weight of the body inverter to find out this that will be a true weight true weight of the body minus upthrust so what's the true weight it is 35 and what 3.5 so what is the upthrust it is nearly 1 so when we subtract this we'll get 2.5 k g f so this is the apparent weight of the body hope you understand this video if you like my video please subscribe to another channel and if you have any doubts you can keep a message in comment box thank you"
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