Estimating Car Weight from Tire Pressure

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A_Munk3y
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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.


Homework Equations



F= ma ?
W1 = P1A1 ?

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
 
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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:)
A_Munk3y said:
… 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:
 


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

tiny-tim said:
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 isn't it :redface:

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

240Kpa x 1000 pa/kpa = 240,000 pa240,000 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 don't add it?)
so its 240,000 = 9.8m/.088m2
m= 2155.1 kg?
 
Last edited:
Hi A_Munk3y! :smile:

(just got up :zzz: …)
A_Munk3y said:
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:)
 
tiny-tim said:
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:
 
ok! w000t!
thank you so much :)