Question

A piece of brass (alloy of copper and zinc) weighs 12.9 g in air. When completely immersed in water it weighs 11.3 g. what is the mass of copper contained in the alloy? Specific gravities of copper and zinc are 8.9 and 7.1 respectively.    

Solution

Correct option is

7.61 g

 

If the alloy contains m g of copper, the amount of zinc in it will be (12.9 –mg. So the volumes of copper and zinc will be respectively 

       

and hence, the total volume of alloy,

       

             

Now as the weight of alloy in air and water is 12.9 g and 11.3 g respectively,     

       

   

Substituting V from eq. (2) in (i) and solving for m, we get 

         m = 7.61 g.

SIMILAR QUESTIONS

Q1

A barge filled with garbage has a density of 800 kg/m3. What present of the barge’s volume is above the water line? The volume below the water line is called the draft of the ship.    

Q2

A king order for a gold crown having a mass of 2 kg. When it arrives from the goldsmith, the volume of the crown is found to be 200 cm3. What is your opinion about the crown if the density of the pure gold is ? 

Q3

 

If a room has dimensions , what is the mass of air in the room if density of air at NTP is 1.3 kg/m3?

[Density of water is 103 kg/m3 and g = 10 m/s2]

Q4

What force  does water exert on the base of a house tank of base area 1.5 m2 when it is filled with water up to a height of 1 m? [Density of water is 103 kg/m3 and g = 10 m/s2

Q5

When equal volumes of two metals are mixed together, the specific gravity of alloy is 4. When equal masses of the same two metals are mixed together, the specific gravity of the alloy is 3. Calculate the specific gravity of each metal.    

Q6

An open end wide tube is immersed vertically in mercury in such a way that a length 0.05 m extends above the mercury level. The open end of the tube is then closed and the tube is raised further by 0.43 m. Calculate the length of the air column above the mercury level in the tube.

                                                                         

Q7

 

A balloon filled with hydrogen has a volume of 1 m3 and its mass is 1 kg. What would be the volume of block of a very light material which it can just lift?

[Density of material of block is 91.3 kg/m3 and that of air is 1.3 kg/m3]  

Q8

A certain block weighs 15 N in air. It weighs 12 N when immersed in water. When immersed in another liquid, it weighs 13 N? Calculate the relative density of (a) the block (b) the other liquid.

Q9

A piece of copper having an internal cavity weighs 264 g in air and 221 g in water. Find the volume of the cavity. Density of copper is 8.8 g/cc.

Q10

In English the phrase ‘tip of the iceberg’ is used to mean a small visible fraction of something that is mostly hidden. For a real iceberg what is this fraction if the density of sea water is 1.03 g/cc and that of ice is 0.92 g/cc?