Mechanics

61.If the diameter of the capillary is doubled, then the height of the water surface rising in it –
 
A. Doubles up
 
B. Remains half
 
C. Remains the same
 
D. Becomes zero
 
Option”B” is correct.
Radius of a capillary tube is inversely proportional to the height of the liquid column. So, if radius of the tube is doubled, rise of level of water will becomes half of the previous rise in capillary tube.
62.The unit of viscosity is-
 
A. Pwize
 
B. Pascal
 
C. Poijuli
 
D. None of these
 
Option”A” is correct.
The unit of viscosity is newton-second per square metre, which is usually expressed as pascal-second in SI units
63.When two capillaries of different diameters are immersed vertically in a liquid, the height of the liquid
 
A. Will be more in both capillaries
 
B. Larger diameter capillary will have more
 
C. Smaller diameter capillary will have more
 
D. Depends on the mass of water
 
Option”C” is correct.

We have the equation for height of capillary rise,
 
 
 
where,
 
 is the elevation of the liquid
 
 is the angle of contact of the liquid with the capillary tube
 
 is the density of the liquid
 
 is the standard acceleration due to gravity
 
 is the radius of the capillary tube
 
From the above equation we can say that the height of capillary rise is inversely proportional to the radius or diameter. So, if two capillary tubes of different diameters are dipped in water, the rise of water is more in tube of smaller diameter.

64.What causes oil to rise in the wick of the lamp?
 
A. Pressure difference
 
B. Capillary phenomenon
 
C. Low oil viscosity
 
D. Carboxylic group in oil
 
Option”B” is correct.
Due to presence of pores (narrow spacings) in the wick, capillary action takes place, which makes the oil to rise in the wick.
65.An iron needle sinks in water but a ship floats, it is based on the principle-
 
A. Pascal’s principle
 
B. Archimedes’ principle
 
C. Kepler’s theory
 
D. Law of gravity
 
Option”B” is correct.
As the density of an iron nail is more than that of water, the nail sinks in water. But a huge ship made of iron floats. This is because of its shape. A ship is hollow in the middle. When the ship is in water the entire volume of the ship, including the hollow portion, displaces water to make space for itself. The volume of water displaced is much greater than the volume of the iron ship. Hence, according to Archimedes’ principle, the upthrust is more than the weight of the ship. That is why the iron ship floats in water.
66.Archimedes’ law is related to which of the following
 
A. Law of flotation
 
B. Right triangle law
 
C. Law of gravity
 
D. Relationship between current and voltage
 
Option”A” is correct.
Archimedes’ principle deals with the forces applied to an object by fluids surrounding it. This applied force reduces the net weight of the object submerged in a fluid.
67.When an object is fully or partially immersed in a liquid, it appears to lose some weight and the apparent loss in weight is equal to the weight of the liquid displaced by the object.
 
A. Bernoulli’s principle
 
B. Archimedes principle
 
C. Pascal’s principle
 
D. Hooke’s law
 
Option”B” is correct.
It’s because of upthrust (also called buoyant force). According to the Archimedes’ principle, any object, partially or fully immersed in a fluid, experiences an upthrust equal to the weight of the fluid displaced by the object.
68.The scientist concerned with buoyancy is
 
A. Archimedes
 
B. Newton
 
C. Louis Pasteur
 
D. All of these
 
Option”A” is correct.
Archimedes’ principle states: An object immersed in a fluid experiences a buoyant force that is equal in magnitude to the force of gravity on the displaced fluid.
69.The amount of buoyancy obtained by a solid partially or completely immersed in a liquid depends on-
 
A. On the amount of liquid displaced by the solid
 
B. On the mass of the solid
 
C. On weight of solid
 
D. None of these
 
Option”A” is correct
70.The reason why a piece of iron does not float on the surface of water is-
 
A. The volume of displaced water is less than the volume of iron
 
B. The weight of water displaced by iron is more than the weight of iron.
 
C. The weight of water displaced by iron is equal to the weight of iron.
 
D. It does not displace water
 
Option”A” is correct.

 The density of iron is more than the density of water therefore the weight of the nail is more than the upthrust experienced by it causing it to sink.

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