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## Friday, October 2, 2015

### Floatation_Class-9 important solved Questions from previous year CBSE Board Paper

Fully Solved Questions from previous year board Paper
Question: 1. What causes buoyant force (or up thrust) on a boat?

Answer: Buoyant force is due to volume of boat and density of water.

Question: 2. what is the cause of buoyant force?

Answer: : The pressure difference on lower part and upper part of a body cause of buoyant force .

Question: 3. An Object of volume V is immersed in a liquid of density P. Calculate the magnitude of buoyant force acting on the object due to the liquid

Question: 4. why does a block of wood held under water rise to the surface when released?

Answer: This happens because as upward force is greater than the weight.

Question: 5. What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid. When does the buoyant force become maximum?

Answer: The buoyant force exerted by a fluid is equal to the weight of fluid displaced. Therefore the buoyant force increases as more and more volume of a solid object is immersed in a liquid.
Buoyant force is maximum when a body is completely immersed in a fluid.

Question: 6. Explain why, a piece of glass sinks in water but it floats in mercury.

Answer: The density of glass is more than water, but less then mercury, Therefore glass float on mercury and sinks in water.

Question: 7. When is the pressure on the ground more when a man is walking or when a man is standing ? Explain.

Answer :  When a man is walking is weight is alternately on one feet or the other, when he is standing, his weight is divided on both feet. Therefore pressure is more on the ground when he is walking (as surface area is less).

Question: 8.  A solid weighs 80 g in air, 64 g in water. Calculate the relative density of solid. When kept in water, state if the object would float or sink?

Answer:  Weight loss in water = (80 -  64) g = 16
Relative density of solid = (weight in air/ Weight loss in water) = 80/16= 5
Since relative density of water is 1 which is less than that of solid. Hence Solid Sink

Question: 9. why density varies?

Answer: The density of a material depends on two things.
(i) The individual mass of each atom or molecule of substance  (ii) How tightly the atoms are packed

Question: 10. An object is suspended with a string . The string is stretched. When the object is completely immersed in water, the extension of the thread decreases. Why?

Answer : This happen because when the object is completely immersed in water it experience an upward force that cause weight loss.
More Questions are solved Here:  http://jsuniltutorial.weebly.com/