A weightless rubber balloon has 100 gm of liquid of density 2 gm/cc and is suspended by a string. What will be the tension in the string when balloon is fully immersed in water?

                      

Mass  of liquid  =  100 gm
Density of liquid = 2 gm/cc

    Volume of ballon containing liquid = 50cc  

When it is fully immeresed in water, it will displace 50cc of water.

Therefore upward thrust on ballon is given by, 

                   U = 50 x 1
                      = 50 gmf 

Tension in string is, 

                   T=100 - 50
                     = 50 gmf



205 Views

The dimensions of the base of a boat are 3.3mx2.2m. When the man gets on to the boat, the boat sinks by 1 cm. What is the mass of the man?

The dimensions of the base of a boat are 3.3 m ×2.2 m

The boat sinks by 1 cm, therefore volume of water displaced when man gets on the boat is,

            V = 3.3 x 2.2 x 0.01

               = 72.6 x 10-3  m

Mass of water displaced = 72.6 x 10-3 x 1000 = 72.6  kg

The man is in a floating state int he boat.

Therefore,

Mass of man = Mass of water displaced
                    = 72.6 kg. 
201 Views

Advertisement

(a) Ice floats in water with about nine-tenth of its volume submerged. What is the fractional volume submerged for an iceberg floating on a fresh water lake of (hypothetical) a planet whose gravity is ten times that of the earth?

(b) What is the fractional volume submerged of an ice-cube in a pail of water placed in an enclosure which is freely falling under gravity?


(a) Let a be the density of ice and ρ be the density of water.

The ice floats in water.

Therefore, weight of ice is equal to the weight of liquid displaced.

Let the volume of ice be V and volume of water displaced be V'.



i.e. fractional volume displaced by ice is independent of g.

Therefore, on the new hypothetical planet, fractional volume displaced by ice is also same as that on the earth i.e. nine-tenth.

(b) In free falling state, ice-cube is in weightlessness state and also the thrust exerted by water is zero. Therefore, it can float with any volume submerged.

338 Views

Advertisement
Why do the hairs of a shaving brush cling together when taken out of water?

The hairs of a shaving brush cling together when taken out of water as a result of surface tension. The free surface of water tries to acquire a minimum surface area. 
254 Views

How does the fractional volume submerged of the floating body change with acceleration due to gravity?

Let a body of volume V and density σ float in a liquid of density ρ

According to the law of floatation, 

Weight of body = Weight f liquid displaced

i.e.           Vσg = V' ρg

where v' is the volume of liquid displaced.

"
 
Fractional volume submerged, 

              V'V=σρ

Since it is independent of g, therefore, the fractional volume submerged of the floating body does not change with acceleration due to gravity.
243 Views

Advertisement