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Gauge pressure

  • Thread starter A_Munk3y
  • Start date
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1. Homework Statement
The gauge pressure in each of the four tires of an automobile is 240 kPa. If each tire has a "footprint" of 220 cm2, estimate the mass of the car.


2. Homework Equations

F= ma ?
W1 = P1A1 ?
3. The Attempt at a Solution

total weight = W1+W2+W3+W4 = P(A1+A2+A3+A4) <------- since all tires have same surface area and same pressure.

240pka(2.2m^3 x 4) = 2112 kg??

dont think i did that right
 

kuruman

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You are confusing gauge pressure and absolute pressure. Look up the definition of gauge pressure.
 

tiny-tim

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Welcome to PF!

Hi A_Munk3y! Welcome to PF! :smile:

(try using the X2 tag just above the Reply box :wink:)
… If each tire has a "footprint" of 220 cm2, estimate the mass of the car.

240pka(2.2m^3 x 4) = 2112 kg??

dont think i did that right
erm :redface: … 220 cm2 = 220 m2/? :smile:
 
72
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Re: Welcome to PF!

You are confusing gauge pressure and absolute pressure. Look up the definition of gauge pressure.
P = F/A ---- is that it?

Hi A_Munk3y! Welcome to PF! :smile:

(try using the X2 tag just above the Reply box :wink:)


erm :redface: … 220 cm2 = 220 m2/? :smile:

its 220 cm2 = 0.022m2 isnt it :redface:

ok let me try this again :P
 
Last edited:
72
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attempt 2
Pressure = Force/Area = Mg/Area = Pa
kPa= = 1000 pa

240Kpa x 1000 pa/kpa = 240,000 pa


240,000 pa x 4 tires = 9.8 x m/ 880cm2(1/100)2

960,000 = 9.8m/0.088m2

or does the pressure remain 240000 (you dont add it?)
so its 240,000 = 9.8m/.088m2
m= 2155.1 kg?
 
Last edited:

tiny-tim

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Hi A_Munk3y! :smile:

(just got up :zzz: …)
240pka(2.2m^3 x 4) = 2112 kg??
hmm … you're really not good at units, are you? :wink:

how about kN instead of kg? :smile:
(that slipped past me last night! :rolleyes:)
 
72
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Hi A_Munk3y! :smile:

(just got up :zzz: …)


hmm … you're really not good at units, are you? :wink:

how about kN instead of kg? :smile:
(that slipped past me last night! :rolleyes:)
nope, i completely suck at units!!! >:(

so you mean 240,000 = 9.8m/.088m2 is still not right ? :frown:
 

tiny-tim

Science Advisor
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ah, you did put the 9.8 in in post #5 …

yes, m = 240 x 88 / 9.8 = 2155 kg looks right (and I think 2000 kg is a fairly average car weight in the USA). :smile:
 
72
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ok! w000t!
thank you so much :)
 

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