PhysicsFlame Institute

18. A rectangular block is 5 cm × 5 cm × 10cm in size. The block is floating in water with 5 cm side vertical. If it floats with 10 cm side vertical, what change will occur in the level of water?

(a) No change (b) It will rise (c) It will fall (d) It may rise or fall depending on the density of block Explanation- (a) Since no change in volume of displaced water takes place, hence level of water remains …

6. A liquid is coming out from a vertical tube. The relation between the weight of the drop W, surface tension of the liquid T and radius of the tube r is given by, if the angle of contact is zero

(a) w= πr2T (b) w= 2πrT (c)w= 2πr2T (d) w= (3/4)πr3 T Ans. b (4)

7. The parts of motor cars are polished by chromium because the angle of contact between water and chromium is

(a) 0o (b) 90o (c) Less than 90o (d) Greater than 90o Ans. d (5)

17. A small sphere of mass m is dropped from a great height. After it has fallen 100 m, it has attained its terminal velocity and continues to fall at that speed. The work done by air friction against the sphere during the first 100 m of fall is

(a) Greater than the work done by air friction in the second 100 m (b) Less than the work done by air friction in the second 100 m (c) Equal to 100 mg (d) Greater than 100 mg Answer-b (11)

16. Spherical balls of radius ‘r’ are falling in a viscous fluid of viscosity

‘η‘ with a velocity ‘v‘. The retarding viscous force acting on the spherical ball is (a) Inversely proportional to ‘r‘ but directly proportional to velocity ‘v‘ (b) Directly proportional to both radius ‘r‘ and velocity ‘v‘ (c) Inversely proportional to …

15. A square plate of 0.1 m side moves parallel to a second plate with a velocity of 0.1 m/s, both plates being immersed in water. If the viscous force is 0.002 N and the coefficient of viscosity is 0.01 poise, distance between the plates in m is

(a) 0.1 (b) 0.05 (c) 0.005 (d) 0.0005 Answer-d (2)

13. A cylindrical tank has a hole of 1 cm2 in its bottom. If the water is allowed to flow into the tank from a tube above it at the rate of

70 cm3/sec. then the maximum height up to which water can rise in the tank is (a) 2.5 cm (b) 5 cm (c) 10 cm …

13. There is a hole of area A at the bottom of cylindrical vessel. Water is filled up to a height h and water flows out in t second. If water is filled to a height 4h, it will flow out in time equal to

(a) t (b) 4t (c) 2 t (d) t/4 Answer-c (8)

12. There is a hole in the bottom of tank having water. If total pressure at bottom is 3 atm

(1 atm = 105N/m2) then the velocity of water flowing from hole is (a) √400 m/s (b) √600 m/s (c) √60 m/s …

11. A cylinder of height 20 m is completely filled with water. The velocity of efflux of water (in m/s) through a small hole on the side wall of the cylinder near its bottom is

(a) 10 (b) 20 (c) 25.5 (d) 5 Answer-b (4)

10. A large tank filled with water to a height ‘h’ is to be emptied through a small hole at the bottom. The ratio of time taken for the level of water to fall from h to h/2 and from h/2 to zero is

(a) √2 (b) 1/ √2 (c) √2 -1 (d) 1/(√2 …

8. A manometer connected to a closed tap reads

3.5 × 105 N/m2. When the valve is opened, the reading of manometer falls to 3.0 × 105 N/m2, then velocity of flow of water is (a) 100 m/s (b) 10 m/s (c) 1 m/s …

10. The radius of a soap bubble is increased

from (1/√π) cm to (2/√π) cm. If the surface tension of water is 30 dynes per cm, then the work done will be (a) 180 ergs (b) 360 ergs (c) 720 ergs (d) 960 ergs Ans. c (12)

5. Water is moving with a speed of

5.18 ms–1 through a pipe with a cross-sectional area of 4.20 cm2. The water gradually descends 9.66 m as the pipe increase in area to 7.60 cm2. The speed of flow at the lower level is (a) 3.0 ms–1 (b) …

5. Radius of a soap bubble is ‘r’, surface tension of soap solution is T. Then without increasing the temperature, how much energy will be needed to double its radius

(a) 4πr2T (b) 2 πr2T (c) 12 πr2T (d) 24 πr2T Ans. d (43)

10. Air is streaming past a horizontal air plane wing such that its speed in 120 m/s over the upper surface and 90 m/s at the lower surface. If the density of air is 1.3

kg per metre3 and the wing is 10 m long and has an average width of 2 m, then the difference of the pressure on the two sides of the wing of (a) 4095.0 Pascal (b) 409.50 Pascal (c) 40.950 …

16. If the surface tension of a liquid is T, the gain in surface energy for an increase in liquid surface by A is

(a) AT-1 (b) AT (c) A2T (d) A2T2 Ans. b (5)

15. If two identical mercury drops are combined to form a single drop, then its temperature will

(a) Decrease (b) Increase (c) Remains the same (d) None of the above Ans. b (3)

14. The work done in blowing a soap bubble of radius r of the solution of surface tension T will be

(a) 8πr2T (b) 2πr2T (c) 4πr2T (d) (4/3)πr2T Ans. a (5)

13. A spherical drop of oil of radius 1 cm is broken into 1000 droplets of equal radii. If the surface tension of oil is 50 dynes/cm, the work done is

(a) 18 π ergs (b) 180 π ergs (c) 1800 π ergs (d) 8000 π ergs Ans. c (4)

12. If work W is done in blowing a bubble of radius R from a soap solution, then the work done in blowing a bubble of radius 2R from the same solution is

(a) W/2 (b) 2W (c) 4W (d) (7/3) W Ans. c (29)

11. The surface tension of a liquid is 5 N/m. If a thin film of the area 0.02 m2 is formed on a loop, then its surface energy will be

(a) 5 x 102 j (b) 2.5 x 10-2 j (c) 2 x 10-1 (d) 5 x 10-1 j Ans. c (5)

9. If T is the surface tension of soap solution, the amount of work done in blowing a soap bubble from a diameter D to 2D is

(a) 2 πD2T (b) 4 πD2T (c) 6 πD2T (d) 8 πD2T Ans. c (9)

8. The amount of work done in blowing a soap bubble such that its diameter increases from d to D is (T= surface tension of the solution)

(a) 4π(D2-d2)T (b) 8π(D2-d2)T (c) π(D2-d2)T (d) 2π(D2-d2)T Ans. d (7)

7. A spherical liquid drop of radius R is divided into eight equal droplets. If surface tension is T, then the work done in this process will be

(a) 2 πR2T (b) 3 πR2T (c) 4 πR2T (d) 2 πR2T Ans. c (31)

7. In the following fig. is shown the flow of liquid through a horizontal pipe. Three tubes A, B and C are connected to the pipe. The radii of the tubes A, B and C at the junction are respectively 2 cm, 1 cm and 2 cm. It can be said that the

(a) Height of the liquid in the tube A is maximum (b) Height of the liquid in the tubes A and B is the same (c) Height of the liquid in all the three tubes is the same (d) Height …