IX Floatation Very Short answer Questions (1 Mark)
1. Give reason why, a block of plastic when released under water comes
up to the surface of water.
Ans: It is because of
buoyancy force
2. Define density. What is the SI unit of density?
Ans: Mass per unit
volume of a substance is called density.
The SI unit of
density is kg/m3 or gm/cm3
3. Name and define SI unit of pressure.
Ans: Pascal or n/m2
1 Pascal is the
pressure act when 1 N force acts perpendicular
on unit area.
4. What do you understand by the term buoyancy?
Ans: Tendency of
fluid to exert an upward force when a body is immersed in to it is called buoyancy
5. Why does a mug full of water feel lighter inside water?
Ans: a mug full of
water feels lighter inside water because of buoyancy force
6. A perpendicular force of 50 N acting on a surface generates a
pressure of 250 Pa. Calculate the area of cross-section of the surface on which
pressure is acting.
Ans: p = F/A Þ A = F/p Þ 50 N/250 Pa = 0.2 m2
7. What is a lactometer used for?
Ans: lactometer used
for finding purity of milk
8. State the unit of density and relative density in SI system.
Ans: The unit of
density is kg/m3
There is no unit of
relative as it is ratio of same physical quantity.
9. State Archimedes’ principle.
Ans: When a body is immersed partially or completely in a
fluid (liquid or gas), it experiences an up thrust or buoyant force which is
equal to the weight of the fluid displaced by the body.
10. What is meant by buoyant force?
Ans: if a body is immersed partially or completely
in a fluid, it experiences an up thrust called buoyant force.
11. A cork floats while the nail sinks in water. Give reason.
Ans: Weight of cork is
less than buoyant force acting on it so
it floats Where as : Weight of the nail is
more than buoyant force acting on it so
it sink
12. What is the principle of floatation?
Ans: A body floats is
a liquid if weight of the liquid displaced by the immersed portion of the body
is equal to the weight of the body.
13. A body of mass 400 g has a volume of 300 cm3. Will body
sink in water or not? [Density of water = 1000 kgm–3]
Ans: density of body =m/v= 400/300=1.3gm/cm3 which
is greater than density of water 1gm/cm3
Hence, Body will sink in water.
14. When we
stand on loose sand, our feet go deep into the sand. But when we lie down on the
sand our body does not go that deep in the sand. Why?
Ans: when we lie down
on the sand our body exert same force on large are that reduce pressure and our
body does not go that deep in the sand.
15. Why is
it easy to walk on sand with flat shoes, then with high heel shoes?
Ans: flat shoes exert
force on large surface area and less force act on sand this make easy to walk
on sand
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