推 mantour:話說這個板看的人據說不多是吧… 01/11 11:57
推 aoeandy:這本書的書皮是綠色的? 01/11 22:50
抱歉...我不是這裡的學生...想問問你們普物的問題
拜託幫幫忙了...我連題目都看不懂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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