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Best of Luck Q1. Hairs of shaving brush cling together when it is removed from water due to- (a) force of attraction between hair (b) surface tension (c) viscosity of water (d) characteristic property of hair Q2. Coatings used on raincoat are waterproof because they - (a) increases angle of contact (b) decreases angle of contact (c) does not alters angle of contact (d) forms a smooth surface Q3. A body measures 5 N in air and 2 N when put in water. The buoyant force is- (a) 7 N (b) 9 N (c) 3 N (d) None of these Q4. A hole is made at the bottom of the tank filled with water (density = 1000 kg/m³). If the total pressure at the bottom of the tank is three atmospheres (1 atmosphere = 10⁵ N/m²), then the velocity of efflux is nearest to- (a) 20 m/s (b) 10√2 m/s (c) 20√2 m/s (d) √500 m/s Q5. When the temperature is increased the angle of contact of a liquid? (a) increases (b) decreases (c) remains the same (d) first increases and then decreases Q6. The surface tension of a soap solution is 2

Q1. Calculate the percentage decrease in the weight of a body when it is taken to a height of 40 km above the Earth's surface. Radius of Earth = 6,400 km Ans. 1.25% Q2. Calculate the depth below the surface of Earth where the acceleration due to gravity is 25% of its value at the Earth's surface. Take, radius of Earth = 6,400 km. Ans. 4.8 × 10⁶ m Q3. A body weighs 100N on Earth's surface. Calculate the gravitational force on the body at a height equal to one-fourth the radius of Earth. Ans. 64 N Q4. Calculate the percentage decrease in weight of a body when taken to a tunnel 38.4 km below the Earth's surface. Ans. 0.6% Q5. Calculate the height from the Earth's surface at which the acceleration due to gravity becomes 75% compared at Earth's surface. Take, radius of Earth = 6,400 km. Ans. 990 km ---------------------------------------------------------------------------------------------- EXTRA QUESTIONS Q6. Find the percentage increase in acceleration due to grav