NCERT Exemplar: Mechanical Properties of Fluids | Physics Class 11 - NEET PDF Download

 Page 1


  
 
     
  
 
Mechanical Properties of Fluids 
 
Exercise 
MULTIPLE CHOICE QUESTIONS-I 
1. A tall cylinder is filled with viscous oil. A round pebble is dropped from 
the top with zero initial velocity. From the plot shown in Figure, indicate 
the one that represents the velocity v of the pebble as a function of time (t). 
 
Ans: (c): When the pebble is dropped from the top of the cylinder filled 
with viscous oil, pebble falls under gravity with constant acceleration, but 
as it is dropped, it enters in oil and dragging force ?? = 6?????? due to 
viscosity of the oil so acceleration decreases from g to zero i.e., velocity 
increases, but acceleration decreases, when acceleration decreased to zero, 
Page 2


  
 
     
  
 
Mechanical Properties of Fluids 
 
Exercise 
MULTIPLE CHOICE QUESTIONS-I 
1. A tall cylinder is filled with viscous oil. A round pebble is dropped from 
the top with zero initial velocity. From the plot shown in Figure, indicate 
the one that represents the velocity v of the pebble as a function of time (t). 
 
Ans: (c): When the pebble is dropped from the top of the cylinder filled 
with viscous oil, pebble falls under gravity with constant acceleration, but 
as it is dropped, it enters in oil and dragging force ?? = 6?????? due to 
viscosity of the oil so acceleration decreases from g to zero i.e., velocity 
increases, but acceleration decreases, when acceleration decreased to zero, 
  
 
     
velocity becomes constant (terminal velocity). These conditions are 
verified in option (c). 
 
2. Which of the following diagrams (Figure) does not represent a 
streamline flow? 
 
Ans: (d): In streamlined flow, the velocity of the fluid at any given point 
remains constant (at a particular line) across any cross-sectional area. 
Hence is streamline flow layers do not cross each other. Hence option (d) 
is not streamlined. 
 
3. Along a streamline 
(a) the velocity of a fluid particle remains constant. 
(b) the velocity of all fluid particles crossing a given position is constant. 
(c) the velocity of all fluid particles at a given instant is constant. 
(d) the speed of a fluid particle remains constant 
Ans: (b): In streamline flow, the speed at a point in a cross-section is 
always constant because Av = constant. Hence, verifies the option only 
(b). 
 
4. An ideal fluid flows through a pipe of circular cross-section made 
of two sections with diameters 2.5cm and 3.75cm. The ratio of the 
velocities in the two pipes is 
(a) 9:4 
Page 3


  
 
     
  
 
Mechanical Properties of Fluids 
 
Exercise 
MULTIPLE CHOICE QUESTIONS-I 
1. A tall cylinder is filled with viscous oil. A round pebble is dropped from 
the top with zero initial velocity. From the plot shown in Figure, indicate 
the one that represents the velocity v of the pebble as a function of time (t). 
 
Ans: (c): When the pebble is dropped from the top of the cylinder filled 
with viscous oil, pebble falls under gravity with constant acceleration, but 
as it is dropped, it enters in oil and dragging force ?? = 6?????? due to 
viscosity of the oil so acceleration decreases from g to zero i.e., velocity 
increases, but acceleration decreases, when acceleration decreased to zero, 
  
 
     
velocity becomes constant (terminal velocity). These conditions are 
verified in option (c). 
 
2. Which of the following diagrams (Figure) does not represent a 
streamline flow? 
 
Ans: (d): In streamlined flow, the velocity of the fluid at any given point 
remains constant (at a particular line) across any cross-sectional area. 
Hence is streamline flow layers do not cross each other. Hence option (d) 
is not streamlined. 
 
3. Along a streamline 
(a) the velocity of a fluid particle remains constant. 
(b) the velocity of all fluid particles crossing a given position is constant. 
(c) the velocity of all fluid particles at a given instant is constant. 
(d) the speed of a fluid particle remains constant 
Ans: (b): In streamline flow, the speed at a point in a cross-section is 
always constant because Av = constant. Hence, verifies the option only 
(b). 
 
4. An ideal fluid flows through a pipe of circular cross-section made 
of two sections with diameters 2.5cm and 3.75cm. The ratio of the 
velocities in the two pipes is 
(a) 9:4 
  
 
     
(b) 3:2 
(c) v?? : v?? 
(?? ) v?? : v?? 
Ans: (a): According to continuity equation (Law of Conservation of mass) 
?? 1
?? 1
= ?? 2
?? 2
 
 
 
 
or ?? 1
: ?? 2
? 9: 4  
Which verifies option (a). 
 
5. The angle of contact at the interface of water-glass is ?? °, 
Ethylalcohol-glass is ?? °, Mercury-glass is ?????? °, and Methyliodide 
glass is ???? °. A glass- capillary is put in a trough containing one of 
these four liquids. It is observed that the meniscus is convex. The 
liquid in the trough is: 
 
Page 4


  
 
     
  
 
Mechanical Properties of Fluids 
 
Exercise 
MULTIPLE CHOICE QUESTIONS-I 
1. A tall cylinder is filled with viscous oil. A round pebble is dropped from 
the top with zero initial velocity. From the plot shown in Figure, indicate 
the one that represents the velocity v of the pebble as a function of time (t). 
 
Ans: (c): When the pebble is dropped from the top of the cylinder filled 
with viscous oil, pebble falls under gravity with constant acceleration, but 
as it is dropped, it enters in oil and dragging force ?? = 6?????? due to 
viscosity of the oil so acceleration decreases from g to zero i.e., velocity 
increases, but acceleration decreases, when acceleration decreased to zero, 
  
 
     
velocity becomes constant (terminal velocity). These conditions are 
verified in option (c). 
 
2. Which of the following diagrams (Figure) does not represent a 
streamline flow? 
 
Ans: (d): In streamlined flow, the velocity of the fluid at any given point 
remains constant (at a particular line) across any cross-sectional area. 
Hence is streamline flow layers do not cross each other. Hence option (d) 
is not streamlined. 
 
3. Along a streamline 
(a) the velocity of a fluid particle remains constant. 
(b) the velocity of all fluid particles crossing a given position is constant. 
(c) the velocity of all fluid particles at a given instant is constant. 
(d) the speed of a fluid particle remains constant 
Ans: (b): In streamline flow, the speed at a point in a cross-section is 
always constant because Av = constant. Hence, verifies the option only 
(b). 
 
4. An ideal fluid flows through a pipe of circular cross-section made 
of two sections with diameters 2.5cm and 3.75cm. The ratio of the 
velocities in the two pipes is 
(a) 9:4 
  
 
     
(b) 3:2 
(c) v?? : v?? 
(?? ) v?? : v?? 
Ans: (a): According to continuity equation (Law of Conservation of mass) 
?? 1
?? 1
= ?? 2
?? 2
 
 
 
 
or ?? 1
: ?? 2
? 9: 4  
Which verifies option (a). 
 
5. The angle of contact at the interface of water-glass is ?? °, 
Ethylalcohol-glass is ?? °, Mercury-glass is ?????? °, and Methyliodide 
glass is ???? °. A glass- capillary is put in a trough containing one of 
these four liquids. It is observed that the meniscus is convex. The 
liquid in the trough is: 
 
  
 
     
(a) water 
(b) ethyl alcohol 
(c) mercury 
(d) methyl iodide 
Ans: (c): Meniscus of liquid is convex so the angle of contact will be the 
obtuse angle that happens in the case of mercury-glass. Hence, verifies the 
option only (c). 
 
MULTIPLE CHOICE QUES TIONS - II 
6. For a surface molecule 
(a) the net force on it is zero. 
(b) there is a net downward force. 
(c) the potential energy is less than that of a molecule inside. 
(d) the potential energy is more than that of a molecule inside. 
Ans: (b, d): Fig. (b) A molecule viewed from the top to the surface of the 
fluid. Force exerted on a molecule by all nearby molecules are equal and 
opposite, so the net horizontal component of force is zero. 
 
In fig. (a) as a molecule is viewed horizontally to the surface of fluid a 
vertically downward force acts on molecule due to which it does not escape 
from surface. Hence the right option is (b). 
Page 5


  
 
     
  
 
Mechanical Properties of Fluids 
 
Exercise 
MULTIPLE CHOICE QUESTIONS-I 
1. A tall cylinder is filled with viscous oil. A round pebble is dropped from 
the top with zero initial velocity. From the plot shown in Figure, indicate 
the one that represents the velocity v of the pebble as a function of time (t). 
 
Ans: (c): When the pebble is dropped from the top of the cylinder filled 
with viscous oil, pebble falls under gravity with constant acceleration, but 
as it is dropped, it enters in oil and dragging force ?? = 6?????? due to 
viscosity of the oil so acceleration decreases from g to zero i.e., velocity 
increases, but acceleration decreases, when acceleration decreased to zero, 
  
 
     
velocity becomes constant (terminal velocity). These conditions are 
verified in option (c). 
 
2. Which of the following diagrams (Figure) does not represent a 
streamline flow? 
 
Ans: (d): In streamlined flow, the velocity of the fluid at any given point 
remains constant (at a particular line) across any cross-sectional area. 
Hence is streamline flow layers do not cross each other. Hence option (d) 
is not streamlined. 
 
3. Along a streamline 
(a) the velocity of a fluid particle remains constant. 
(b) the velocity of all fluid particles crossing a given position is constant. 
(c) the velocity of all fluid particles at a given instant is constant. 
(d) the speed of a fluid particle remains constant 
Ans: (b): In streamline flow, the speed at a point in a cross-section is 
always constant because Av = constant. Hence, verifies the option only 
(b). 
 
4. An ideal fluid flows through a pipe of circular cross-section made 
of two sections with diameters 2.5cm and 3.75cm. The ratio of the 
velocities in the two pipes is 
(a) 9:4 
  
 
     
(b) 3:2 
(c) v?? : v?? 
(?? ) v?? : v?? 
Ans: (a): According to continuity equation (Law of Conservation of mass) 
?? 1
?? 1
= ?? 2
?? 2
 
 
 
 
or ?? 1
: ?? 2
? 9: 4  
Which verifies option (a). 
 
5. The angle of contact at the interface of water-glass is ?? °, 
Ethylalcohol-glass is ?? °, Mercury-glass is ?????? °, and Methyliodide 
glass is ???? °. A glass- capillary is put in a trough containing one of 
these four liquids. It is observed that the meniscus is convex. The 
liquid in the trough is: 
 
  
 
     
(a) water 
(b) ethyl alcohol 
(c) mercury 
(d) methyl iodide 
Ans: (c): Meniscus of liquid is convex so the angle of contact will be the 
obtuse angle that happens in the case of mercury-glass. Hence, verifies the 
option only (c). 
 
MULTIPLE CHOICE QUES TIONS - II 
6. For a surface molecule 
(a) the net force on it is zero. 
(b) there is a net downward force. 
(c) the potential energy is less than that of a molecule inside. 
(d) the potential energy is more than that of a molecule inside. 
Ans: (b, d): Fig. (b) A molecule viewed from the top to the surface of the 
fluid. Force exerted on a molecule by all nearby molecules are equal and 
opposite, so the net horizontal component of force is zero. 
 
In fig. (a) as a molecule is viewed horizontally to the surface of fluid a 
vertically downward force acts on molecule due to which it does not escape 
from surface. Hence the right option is (b). 
  
 
     
There is a net attractive force on molecules at the surface acting 
downwards. So, the P.E of molecules at the surface is negative to lower 
ones but in magnitude PE (mgh) is more than that of the lower or inside 
molecules. Thus, this verifies option (d). 
 
7. Pressure is a scalar quantity because 
(a) it is the ratio of force to area and both force and area are vectors. 
(b) it is the ratio of the magnitude of the force to area. 
(c) it is the ratio of the component of the force normal to the area. 
(d) it does not depend on the size of the area chosen. 
Ans: (c): what makes pressure a scalar quantity is the fact that it is the 
component of force along the direction of area that is taken into account while 
defining pressure. Thus, the direction of quantities involved remain fixed and 
pressure becomes a scalar quantity. This verifies (c). 
 
8. A wooden block with a coin placed on its top, floats in water as 
shown in Figure. The distance l and h are shown in the figure. After 
some time the coin falls into the water. Then 
(a) l decreases. 
(b) h decreases. 
(c) l increases. 
(d) h increase. 
Ans: (a, b): According to the law of floatation weight of the floating body is 
equal to the weight of displaced fluid. When a coin falls into the water, the net 
weight of the floating body is decreased so the floating body will displace less 
amount of water so the block rises up and I will decrease. But the height h of 
water will decrease as less water is displaced now. So verifies the option (a, b)