抱歉...我不是这里的学生...想问问你们普物的问题 拜托帮帮忙了...我连题目都看不懂QQ 6.42 (a)calculate the minimum safe distance you can be from a speaker that puts 2.00W of sound ,using the following assumptions :the sound power spreads uniformly over a sphere of radius r and area 4πr2, your eardrum's area is 0.8cm2,and it cannot tolerate more than 0.000001W. Damage is done by this small amount of power after prolonged exposure and can be repaired by the body ,but damage done by 0.0001W (found at many rock concerts) occurs almost instantaneously and prolonged exposure at that level produces permanent damage .(b)Since 2.00W of sound power is very large compared to what the ear can tolerate and since many sound systems can apply more than 100W of electrical power input to a speaker, what can you conclude about the efficiency of a speaker in converting electrical power to sound? 6.59 the swimmer shown in Figure 6.24 exerts an average horizontal backward force of 80N with his arm during each 1.8m long stroke .(a)What is his work output in each stroke ?(b)calculate the power output of his arms if he does 120strokes per minute 6.65 The 70 kg swimmer in Figure 6.24 starts a race with an initial velocity of 1.25m/s and exerts an average force of 80N backward with his arms during each 1.8 m long stroke . (a )what is his initial acceleration if water resistance is 45N ?(b)what is the subsequent average resistance force from the water during the 5.00 s it takes him to reach his top velocity of 2.5m/s ? (c)discuss whether water resistance seems to increase linearly with velocity. --

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