其實我也不確定我的對不對耶囧 3-87 It is said that Archimedes discovered his principle during a bath while thinking about how he could determine if King Hiere's crown was actually made of pure gold. While in the bathtub, he conceived the idea that he could determine the average density of an irregularly shaped object by weighing it in air and also in water. If the crown weighed 3.20 kgf(= 31.4N) in air and 2.95 kgf(= 28.9N) in water, determine if the crown is made of pure gold. The density of gold is 19300 kg/m^3. Discuss how you can solve this problem without weighing the crown in water but by using an ordinary bucket with no calibration for volume. You may weigh anything in air. 3-109 A 3-m-diameter, 7-m-long cylindrical tank is completed filled with water. The tank is pulled by a truck on a level road with the 7-m-long axis being horizontal. Determine the pressure difference between the front and back ends of the tank along a horizontal line when the truck (a) accelerates at 3m/s^2 and (b) decelerates at 4 m/s^2. 3-128 Consider a U-tube filled with mercury except the 18-cm-high portion at the top, as shown in Fig. P3-128. The diameter of the right arm of the U-tube is D = 2 cm, and the diameter of the left arm is twice that. Oil with a specific gravity of 2.72 is poured into the left arm, forcing some mercury from the left arm into the right one. Determine the maximum amout of oil that can be added into the left arm. Fig. P3-128 http://ppt.cc/8JSA 3-141 A semicircular 30-ft-diameter tunnel is to be built under a 150-ft-deep, 800-ft-long lake, as shown in Fig. P3-141. Determine the total hydrostatic force acting on the roof of the tunnel. Fig. P3-141 http://ppt.cc/qSO@ 3-142 A 50-ton, 6-m-diameter hemispherical dome on a level surface is filled with water, as shown in Fig. P3-142. Someone claims that he can lift this dome by making use of Pascal's law by attaching a long tube to the top and filling it with water. Determine the required height of water in the tube to lift the dome. Disregard the weight of the tube and the water in it. Fig. P3-142 http://ppt.cc/0orJ --

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