# Displaced water will be more than the weight of the

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displaced water will be more than the weight of the body; so it will float. If the density of object the is more than that of water, the upward thrust will be smaller than the weight of the body; so it will sink. 1 + 1 = 2 [CBSE Marking Scheme, 2012] 3. (i) Density of iron is more than water, but less than mercury. (ii) To cover more surface area and exert less pressure on the ground. 1 + 1 = 2 [CBSE Marking Scheme, 2012] 4. A bucket full of water when immersed in water experiences an upward buoyant force that reduces its weight, and hence, it feels lighter whereas in air the apparent loss in weight is negligible so we feel its actual weight. 1 + 1 = 2 [CBSE Marking Scheme, 2012]
P-82 S C I E N C E - IX 5. Mass of the block = 2 kg Dimensions = 8 × 5 × 1 \ Thrust = m × g = 2 × 10 = 20 N (i) Area of contact = 5 × 1 cm 2 = 0.0005 m 2 P = F A = 20 0.0005 = 200000 5 = 40000 Pascal. (ii) Area of contact = 8 ×5 = 40 cm 2 = 0.0040 m 2 P = F A = 20 0.0040 = 20000 4 = 5000 Pascal. 6. Pressure = thrust / area 1 pascal is the pressure acting on a surface of area 1 square metre by a thrust of 1 newton. Thrust = Weight of body = 500 N Pressure = thrust/ area = 500/2.5 = 200 Pascal 3 [CBSE Marking Scheme, 2016] 7. Archimedes’ principle states that an object will experience an upward force and displaces the liquid in which it is immersed partially or completely; if the weight of liquid displaced is more than the weight of body, then the body will float. In submarines and ships, the body is designed in such a way that it displaces more water than its weight and hence it floats. Lactometer : to determine the purity of sample of milk, Hydrometer - to determiner the of liquids. 1 + 2 + 2 = 5 WORKSHEET-134 Solutions 1. By making the area half, pressure will be doubled. This is because pressure is the thrust per unit area, i.e ., Pressure = F A Thus, pressure is directly proportional to force and inversely proportional to area. 3 2. A body will float in a liquid if the liquid displaced by the immersed part of the body in liquid is equal to the weight of the body. In case of iron ship, which is hollow from within, the weight of water displaced by the ship is more than the weight of the ship and hence, it does not sink in water. But in case of iron needle which is compact i.e. , not hollow and the density of iron is more than that of the weight of water displaced by iron needle is much less than its own weight. Hence, it sinks in water. 3 3. No, the buoyant force is not same in all fluids for a given body. The buoyant force on the body immersed in a fluid is directly proportional to the density of the fluid in which the body is immersed. Buoyant force on the body = Volume of the body immersed in fluid × Density of the fluid × Acceleration due to gravity ( g ). = 1·8 × 1020 × 10 = 18,360 N. 1 + 2 = 3 4. From the question, Weight of solid X in air (W air ) = 180 g ½ Weight of solid X in water (W water ) = 150 g ½ Relative density of solid (X) = ? As, R.D. of solid = Weight of solid in air Loss of weight of solid in water = 180 180 150 180 30 ( ) - = = 6 2 Therefore, the relative density (R.D.) of X is 6.