Physics Times – July 2019

2.The cylindrical tube of a spray pump has radius
R, one end of which has n fine holes, each of
radius r. If the speed of the liquid in the tube is
v, the speed of the ejection of the liquid through
the holes is [2015]

(a)

3.A wind with speed 40 m/s blows parallel to
the roof of a house. The area of the root is

(^2) R
nr
v
(b)
2
2 2
R
n r
v
(c)
2
2
R
nr
v
(d)
2
3 2
R
n r
v
250m.^2
Assuming that the pressure inside the house
is atmospheric pressure, the force exerted by
the wind on the roof and the direction of the
force will be P 1.2kg / mair^2  [2015]
(a) 4.8 10 N,^5 downwards
(b) 4.8 10 N,^5 upwards
(c) 2.4 10 N,^5 upwards
(d) 2.4 10 N,^5 downwards
SURFACE TENSION
1.Water rises to height ‘h’ in capillary tube. If
the length of capillary tube above the surface
of water is made less than ‘h’ then [2015]
(a)Water rises up to the top of capillary tube
and stays there without overflowing.
(b)Water does not rise at all.
(c)Water rises up to a point a little below the
top and stays there.
(d)Water rises up to the top of capillary tube
and then starts overflowing like a fountain.
2.A certain number of spherical drops of a liquid
of radius r coalesce to form a single drop of
radius R and volume V. If T is the surface
tension of the liquid, then [2014]
(a) Energy
1 1
4VT
r R
  
   is released
(b) Energy
1 1
3VT
r R
  
   is released
(c) Energy
1 1
3VT
r R
  
   is absorbed
(d) Energy is neither released nor absorbed
3.The wettability of a surface by a liquid depends
primarily on [2013]
(a)Angle of contact between the surface and
the liquid
(b) Density
(c) Viscosity
(d) Surface tension

4. Radius of a soap bubble is increased from R
   to 2R. Work done in this process in terms of
   surface tension is [2004]
   (a) 24 R S^2 (b) 48 R S^2
   (c) 12 R S^2 (d) 36 R S^2


5. A capillary tube of radius R is immersed in
   water and water rises in it to a height H. Mass
   of water in the capillary tube is M. If the radius
   of the tube is doubled, mass of water that will
   rise in the capillary tube will now be[2002]
   (a) 2M (b) M (c) M/2 (d) 4M

ELASTICITY

1. d 2. d 3. a 4. c 5. b

FLUID MECHANICS

1. d 2. c 3. c

SURFACE TENSION

1. a 2. b 3. a 4. a 5. a

ELASTICITY

1.Sol: Volume V

2. 
   

[2015]

3. 
   

[2015]

SURFACE TENSION

1. 
   

[2015]

2. 
   

[2014]

3. [2013]

4.

[2004]

5.

[2002]

ELASTICITY

1. 
   
   
   
   2. 
      
      
      
      3. 
         
         
         
         4. 
            
            
            
            5. 
               
            
            
            
            
         
         
         
         
      
      
      
      
   
   
   
   

FLUID MECHANICS

1. 
   
   
   
   2. 
      
      
      
      3. 
         
      
      
      
      
   
   
   
   

SURFACE TENSION

1. 
   
   
   
   2. 
      
      
      
      3. 
         
         
         
         4. 
            
            
            
            5. 
               
            
            
            
            
         
         
         
         
      
      
      
      
   
   
   
   

ELASTICITY

1.Sol:

   A L A L 1 3 2

2 1

3

L

L 

Stress (Y strain)

;

AY

F L

L

  

 

 

3

' 9

3

AY

F L F

L

 

 

   

  

  

  