CBSE
Multiple Choice QuestionsA boat strikes an under water rock which punctures a hole 5 cm in diameter in its hull which is 1.5 m below the water line. At what rate in litre per second does water enter.
2.65 Ls-1
8.85 Ls-1
10.65 Ls-1
624 Ls-1
Two soap bubbles A & B are kept in a closed chamber where the air is maintained at pressure 8 N/m2 . The radii of bubbles A & B are 2cm and 4cm, respectively. Surface tension of the soap water used to make bubbles is 0.04 N/m. If nA and nB are the number of moles of air in bubbles A and B, respectively, then = ?[Neglect the effect of gravity]
2
8
9
6
The surface tension and vapour pressure of water at 20°C is 7.28x10-2 Nm-1 and 2.33 x 103 Pa respectively. The radius of the smallest spherical droplet which can form without evaporating is
6.25 x 10-5 m
6.25 x 10-3 m
7.45 x 10-3 m
8.9 x 10-4 m
By sucking through a straw, a student can reduce the pressure in his lungs to 750 mm of Hg (density 13.6 g/cm3). Using the straw, he can drink water from a glass upto a maximum depth of
10 cm
13.6 cm
75 cm
1.36 cm
A wooden block is floating on water kept in a beaker, 40% of the block is above the water surface. Now the beaker is kept inside a lift that starts going upward with acceleration equal to . The block will then
sink
float with 10% above the water surface
float with 40% above the water surface
float with 70% above the water surface
Water wets the walls of its glass container due to the fact that
cohesive force is greater than adhesive force
cohesive force is equal to the adhesive force
adhesive force is greater than the cohesive force
cohesive and adhesive forces form action-reaction pair
Air of density 1.3 kg/m3 flows horizontally with a speed 106 km/h. A house has a plane roof of area 40 m2. Find the magnitude of aerodynamic lift on the roof.
4.22 × 105 N
2.25 × 104 N
4.22 × 103 N
2.25 × 106 N
Surface tension of a detergent solution is 2.8 x 10-2 Nm-1. The work done in blowing a bubble of diameter 1 cm will be nearly
1.24 x 10-4 J
1.76 × 10-5 J
1.8 × 10-3 J
2.4 x 10-4 J
The neck and bottom of a bottle are3 cm and 15 cm in radius respectively. If the cork is pressed with a force 12 N in the neck of the bottle, then force exerted on the bottom of the bottle is
30 N
150 N
300 N
600 N
A wooden block, with a coin placed on its top, floats in water as shown in the figure. The distances h and l are shown there. After sometime, the coin falls into the water. Then
both l and h increase
both l and h decrease
l decreases and h increases
l increases and h decreases
