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Answers to the Questions

Chapter No. 5

Answer 48

Pressure = Density x Gravity x Height


Density of Water = 1000 Kg/m3

Gravity of Earth = 9.8 m/s2

Height = 50 m

Pressure = 1000 x 9.8 x 50 = 490,000 N/m2

Answer 74

No, the reading does not change. This is because of the fact that a bathroom scale measures force and not the pressure. By switching all the weight from two feet two one, the pressure on the scale is increased though, the force remains the same.

Answer 78

This is because of the fact that sinking and floating of an object does not depend on weight of the object and depends on the density. No matter how much the weight of an object is, if its density is less than that of water, it will float on it, otherwise it will sink. One good example can be that a needle weighing few grams sinks whereas, a ship weighing thousands of tons floats on the water.

Answer 88

The buoyant force depends on the weight of the water displaced by an object. The higher the density of the object is the lower volume it will cover and lower mass of water it will displace and vice versa. Since, the density of Styrofoam is less than that of lead pallets, it will displace more mass of water and therefore, it will have a greater buoyant force. Whereas, lead pallets will displace a very small amount of water and hence, buoyant force will be negligible.

Answer 94

Since, elephant displaces a greater amount of atmosphere than a helium ballon it has a greater buoyant force. Though, as the weight of the elephant is much higher than that of a helium balloon and therefore, the balloon moves easily and not the elephant.

Answer 96

No, the buoyant force depends on the amount of atmosphere displaced by the object and not on the density of the object. Therefore, buoyant force stays the same.

Answer 98

When, the balloon is filled with higher pressure than atmosphere it displaces higher volume of atmosphere and therefore, the buoyant force acting on it is greater. This results in the fact that the mass of the balloon becomes in effective and negligible. When one of the balloon is popped, the buoyant force is removed and hence the mass of the balloon acts on the stick and the stick tilts towards the popped balloon.

Answer 108

The professor is demonstrating the fact that, when a weight is distributed among numerous supports the pressure on each support divides. Therefore, the small pieces of glass don't have the pressure required to penetrate the skin of the professor's feet.

Answer 114

The buoyant force exists because of the fact that, there exists a difference in pressure between the bottom of the submerged object and the pressure on its top. If the pressure in the liquid is same at all depths, there will be no difference and therefore, no buoyant force will exist.

Chapter No. 6

Answer 56

The specific heat capacity of metals is way more than that of ...
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