Advertisements
Advertisements
Question
A solid body weighs 2.10 N. in air. Its relative density is 8.4. How much will the body weigh if placed
(1) in water,
(2) in liquid of relative density 1.2?
Advertisements
Solution
Weight of solid body in air = 2.10 N
R.D. of solid = 8.4
R.D. of solid = `("Density of solid"(rho_"solid"))/"Density of water"`
`8.4 = rho_"solid"/rho_"water"`
`rho_"solid" = 8.4 xx rho_"water" = 8.4 xx 1000 = 8400` kgm-3
(1) R.D. of solid = `"Weight of solid in air"/"Weight of water displaced by body"`
`8.4 = 2.10/"Weight of water displaced by body"`
Weight of water displaced by body = `2.10/8.4 = 0.25` N
Weight of body in water = Weight of body in air – Weight of water displaced by body
= 2.10 - 0.25 = 1.85 N
(2) Upthrust due to water = Weight of water displaced by body
= 0.25 N
Upthrust due to liquid = Upthrust due to water ×R.D. of liquid
= 0.25 x 1.2 = 0.30 N
Weight of body in liquid = Weight of body in air – Upthrust due to liquid
= 2.10-0.30= 1.80 N
APPEARS IN
RELATED QUESTIONS
A body of volume 100 cm3 weighs 5 kgf in air. It is completely immersed in a liquid of density 1.8 × 103 kg m-3. Find:
- The upthrust due to liquid and
- The weight of the body in liquid.
Express the relationship between the C.G.S. and S.I. units of density.
How does the density ρs of a substance determine whether a solid piece of that substance will float or sink in a given liquid ρL?
A man first swims in sea water and then in river water. (i) Compare the weights of sea water and river water displaced by him.
(ii) Where does he find it easier to swim and why?
A sinker is found to weigh 56.7 gf in water. When the sinker is tied to a cork of weight 6 gf, the combination is found to weigh 40.5 gf in water. Calculate R.D. of cork.
A cork cut in the form of a cylinder floats in alcohol of density 0.8 gcm-3, such that 3/4 of its length is outside alcohol. If the total length of the cylinder is 35 cm and area of cross-section 25 cm2, calculate:
(1) density of cork
(2) wt. of cork
(3) extra force required to submerge it in alcohol
An inflated balloon is placed inside a big glass jar which is connected to an evacuating pump. What will you observe when the evacuating pump starts working? Give a reason for your answer.
A body of mass 50 g is floting in water. What is the apparent weight of body in water? Explain your answer.
If 2/3rds of a piece of wood submerges in water and 3/4ths of the same piece of wood submerges in oil. Find the density of the oil.
A wooden cube of side 10 cm has a mass of 700 g. It will float in the water with:
(a) Half of its volume inside the water
(b) 3 cm height above the water surface
(c) 7 cm height above the water surface
(d) Just inside the water surface.
