2022Flame Institute

5. A concrete sphere of radius R has a cavity of radius r which is packed with sawdust. The specific gravities of concrete and sawdust are respectively 2.4 and 0.3 for this sphere to float with its entire volume submerged under water. Ratio of mass of concrete to mass of sawdust will be

(a) 8 (b) 4 (c) 3 (d) Zero Answer-b (7)

4. In making an alloy, a substance of specific gravity and mass is mixed with another substance of specific gravity and mass ; then the specific gravity of the alloy is

s1 and mass m1 is mixed with another substance of specific gravity s2 and mass m2 ; then the specific gravity of the alloy is (a) ( m1 + m2 )/(s1 +s2 ) …

3. A hemispherical bowl just floats without sinking in a liquid of density

1.2 × 103kg/m3. If outer diameter and the density of the bowl are 1 m and 2 × 104 kg/m3 respectively, then the inner diameter of the bowl will be (a) 0.94 m (b) 0.97 m (c) 0.98 m …

2. A log of wood of mass 120 Kg floats in water.

The weight that can be put on the raft to make it just sink, should be (density of wood = 600 Kg/m3) (a) 80 Kg (b) 50 Kg (c) 60 Kg …

1. An ice berg of density

900 Kg/m3 is floating in water of density 1000 Kg/m3. The percentage of volume of ice-cube outside the water is (a) 20% (b) 35% (c) 10% …

31. Radius of an air bubble at the bottom of the lake is r and it becomes 2r when the air bubbles rises to the top surface of the lake. If P cm of water be the atmospheric pressure, then the depth of the lake is

(a) 2p (b) 8p (c) 4p (d) 7p Answer-d (19)

29. Why the dam of water reservoir is thick at the bottom

(a) Quantity of water increases with depth (b) Density of water increases with depth (c) Pressure of water increases with depth (d) Temperature of water increases with depth Explanation- (c) A torque is acting on the wall of the dam …

28. A given shaped glass tube having uniform cross section is filled with water and is mounted on

a rotatable shaft as shown in figure. If the tube is rotated with a constant angular velocity ω then (a) Water levels in both sections A and B go up (b) Water level in Section A goes up and that …

26. Three liquids of densities d,2d and 3d are mixed in equal proportions of weights. The relative density of the mixture is

(a) 11d/7 (b) 18d/11 (c) 13d/9 …

20. If the radius of a soap bubble is four times that of another, then the ratio of their pressures will be

(a) 1 : 4 (b) 4 : 1 (c) 16 : 1 (d) 1 : 16 Ans. a (4)

19. If pressure at half the depth of a lake is equal to 2/3 pressure at the bottom of the lake then what is the depth of the lake

(a) 10m (b) 20m (c) 60m (d) 30m Ans. b (3)

18. There are two liquid drops of different radii. The excess pressure inside over the outside is

(a) More in the big drop (b) More in the small drop (c) Equal in both drops (d) There is no excess pressure inside the drops Ans. b (4)

6. A long cylindrical glass vessel has a small hole of radius ‘r’ at its bottom. The depth to which the vessel can be lowered vertically in the deep water bath (surface tension T) without any water entering inside is

(a) 4T/ ρrg (b) 3T/ρrg (c) 2T/ρrg (d) T/ρrg Ans. c (6)

1. A soap bubble assumes a spherical surface. Which of the following statement is wrong

(a) The soap film consists of two surface layers of molecules back to back (b) The bubble encloses air inside it (c) The pressure of air inside the bubble is less than the atmospheric pressure; that is why the atmospheric …

41. Water rises up to a height h in a capillary tube of certain diameter. This capillary tube is replaced by a similar tube of half the diameter. Now the water will rise to the height of

(a) 4h (b) 3h (c) 2h (d) h Ans. c (3)

38. Kerosene oil rises up the wick in a lantern

(a) Due to surface tension of the oil (b) The wick attracts the kerosene oil (c) Of the diffusion of the oil through the wick (d) None of the above Ans. a (5)

37. In a capillary tube, water rises to 3 mm. The height of water that will rise in another capillary tube having one-third radius of the first is

(a) 1 mm (b) 3 mm (c) 6 mm (d) 9 mm Ans. d (8)

19. A vertical U-tube of uniform inner cross section contains mercury in both sides of its arms. A glycerin

(density = 1.3 g/cm3) column of length 10 cm is introduced into one of its arms. Oil of density 0.8 gm/cm3 is poured into the other arm until the upper surfaces of the oil and glycerin are in the same …

18. The height to which a cylindrical vessel be filled with a homogeneous liquid, to make the average force with which the liquid presses the side of the vessel equal to the force exerted by the liquid on the bottom of the vessel, is equal to

(a) Half of the radius of the vessel (b) Radius of the vessel (c) One-fourth of the radius of the vessel (d) Three-fourth of the radius of the vessel Answer-b (9)

13. The value of g at a place decreases by 2%. The barometric height of mercury

(a) Increases by 2% (b) Decreases by 2% (c) Remains unchanged (d) Sometimes increases and sometimes decreases Answer-a (8)

14. A barometer kept in a stationary elevator reads 76 cm. If the elevator starts accelerating up the reading will be

(a) Zero (b) Equal to 76 cm (c) More than 76 cm (d) Less than 76 cm Answer-d (0)

16. A beaker containing a liquid is kept inside a big closed jar. If the air inside the jar is continuously pumped out, the pressure in the liquid near the bottom of the liquid will

(a) Increases (b) Decreases (c) Remain constant (d) First decrease and then increase Answer-b (3)

17. A barometer tube reads 76 cm of mercury. If the tube is gradually inclined at an angle of 60o with vertical, keeping the open end immersed in the mercury reservoir, the length of the mercury column will be

(a) 152 cm (b) 76 cm (c) 38 cm (d) 38√3 cm Answer-a (2)

21 If two liquids of same masses but densities

ρ1 and ρ2 respectively are mixed, then density of mixture is given by (a) ρ=(ρ1 + ρ2)/2 (b) ρ=(ρ1 + ρ2)/( 2 ρ1 ρ2) (c) …

40. 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

(a) M (b) 2M (c) M/2 (d) 4M Ans. b (36)

39. Water rises against gravity in a capillary tube when its one end is dipped into water because

(a) Pressure below the meniscus is less than atmospheric pressure (b) Pressure below the meniscus is more than atmospheric pressure (c) Capillary attracts water (d) Of viscosity Ans. a (5)

15. A closed rectangular tank is completely filled with water and is accelerated horizontally with an acceleration a towards right. Pressure is (i) maximum at, and (ii) minimum at

(a) (i) B (ii) D (b) (i) C (ii) D (c) (i) B (ii) C (d) (i) B (ii) A Explanation- (a) Due to acceleration towards right, there will be a pseudo force in a left direction. So the pressure …

2. If two soap bubbles of different radii are in communication with each other

(a) Air flows from larger bubble into the smaller one (b) The size of the bubbles remains the same (c) Air flows from the smaller bubble into the large one and the larger bubble grows at the expense of the smaller …

6. The height of a mercury barometer is 75 cm at sea level and 50 cm at the top of a hill. Ratio of density of mercury to that of air is

104. The height of the hill is (a) 250 m (b) 2.5 km (c) 1.25 km (d) 750 m Answer-b …

5. A siphon in use is demonstrated in the following figure. The density of the liquid flowing in siphon is

1.5 gm/cc. The pressure difference between the point P and S will be (a) 105 N/m (b) 2 × 105 N/m (c) Zero (d) Infinity Explanation- (c) As the both points are at the surface of liquid and these points …

3. An inverted bell lying at the bottom of a lake 47.6 m deep has

50 cm3 of air trapped in it. The bell is brought to the surface of the lake. The volume of the trapped air will be (atmospheric pressure = 70 cm of Hg and density of Hg = 13.6 g/cm3)An inverted …