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    1. The envelope of a hot air balloon contains 1500 m3 of hot air of density 0.8 kg/m3. The mass of the balloon ( not including the hot air) is 420 kg. The density of the surrounding air is 1.3 kg/m3. What is the lifting force? a) 3300 N b) 4400 N c) 5500 N d) 6600 N 2. A block of 40 cm3 is floating in oil. If 20 cm3 of the block is immersed in the liquid, find its density in g/cm3? ( doil= 900 kg/m3) a) o.4 b) 0.45 c) 0.9 d) 0.25 1. In a car lift, compressed air exerts a force on a small piston having an area of 300 cm2. What force must the compressed air exert in order to lift a car weighing 12000 N on the big piston, which has an area of 4800 cm2? 2. Half of a spherical ball floats in a liquid of density 1.6 g/cm3. If the volume of the ball is 300 cm3, what is the mass of it? 3. A block of wood of volume 90 cm3 and density 0.6 g/cm3 floats in water. What is the volume immersed in the water? 4. A lead sphere has a total mass of 45.2 kg. If it is put in the water what will be the upthrust force on it? 5. An aluminum cube of side 10 cm is suspended with a spring scale. Next, it is submerged in a container of water, what is the reading on the scale? (dal=2700kg/m3)

    Автор: anakz14 :: 2009-12-29
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    Автор: anakz14 :: 2009-12-28
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    Buoyancy (Archimedes’ Principle): Every fluid applies a buoyant (up-thrust) force on the completely or partly immersed bodies in it. The upthrust force acting on such bodies is a consequence of pressure difference between the upper and lower parts of the object immersed into the fluid due to the depth. As it is observed in the figure the pressure acting on the bottom area is greater than the upper surface since the lower surface is at a level that is deeper than the upper part. Thus, if the top and the bottom areas are considered to be equal there exists a net force acting on the object in the upward direction in accordance with the definition of pressure: P= F/A. Since the pressure values acting on the walls of the object are symmetric, they cancel each other. So they do not have any contribution to buoyant force. Interrogation of new subject : The upthrust force acting on such bodies is a consequence of pressure difference between the upper and lower parts of the object immersed into the fluid due to the depth. As it is observed in the figure the pressure acting on the bottom area is greater than the upper surface since the lower surface is at a level that is deeper than the upper part.
    Автор: anakz14 :: 2009-12-28
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