Floatation class 9th important questions

Om Sai Ram
SPECTRUM CLASSES

Floatation

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 Newton/square meter

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 , A = F/p = 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
Er.Shyam Pachori 
CL 157 D.D Nagar 
Mob.:9039803981