Re: [題目] 白努力定律的題目2

[monmath (烽火狼煙血櫻飄殺)]

※ 引述《topractise (連月亮都幫我!)》之銘言：
: Water pressurized to (3.5 x 10^5) Pa is flowing at 5.0m/s in a horizontal pipe
: which contracts to 1/3 its former area. What are the pressure and velocity of
: the water after the contraction ?
: (A) 2.5 x 10^5 Pa , 15m/s
: (B) 3.0 x 10^5 Pa , 10m/s
: (C) 3.0 x 10^5 Pa , 15m/s
: (D) 4.5 x 10^5 Pa , 1.5m/s
: (E) 5.5 x 10^5 Pa , 1.5m/s
: 請問是A還是C呀...要怎麼算勒

體積不可壓縮：A1*v1=A2*v2

            =>A*5=(1/3)A*v2

            => v2=15

Bernoullie(也許拼錯XD) equation:

P1+(1/2)*d*v1^2=P2+(1/2)*d*v2^2

3.5*10^5+0.5*1000(SI unit)*5^2=P2+(1/2)*1000*15^2

P2=2.5*10^5

so...(A)

算散射算到很煩...= =

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