Physics Question

[Opejay]

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If a solid will buckle under pressure greater than 12atm, and the solid has a specific gravity of 4, what is the maximum height of a circular column made from the solid that can be built at the earth's surface? (Note: 1atm = 101,000 Pa.)

A. 4m
B. 12m
C. 24m
D. 30m

The answer is 30m but I do not understand how it's 30m

Thanks for your help 🙂

 

[Raiden2012]

.

 

[Raiden2012]

Oops, added to many zeros.
I meant 100000Pa

 

[Opejay]

Thanks! how did you get 4000?

 

[Postictal Raiden]

If a solid will buckle under pressure greater than 12atm, and the solid has a specific gravity of 4, what is the maximum height of a circular column made from the solid that can be built at the earth's surface? (Note: 1atm = 101,000 Pa.)

A. 4m
B. 12m
C. 24m
D. 30m

The answer is 30m but I do not understand how it's 30m

Thanks for your help 🙂

pressure = F/A = mg/A

Density = m/v; 4000kg/m^3 = m/V; m = 4000kg/m^3 * V

pressure = (4000kg/m^3 * V * g)/A; volume/area = height; so, 1.2x10^6 = 4000kg/m^3 *g * h

The rest is all arithmetic, solve for h

 

[Raiden2012]

Specific gravity is the ratio of density of substance to density of water
Density of substance = specific gravity of substance X density of water
= 4 X 1000 kg/m3 = ans

 

[Opejay]

Got it now! Thanks!!!

 

[Opejay]

pressure = F/A = mg/A

Density = m/v; 4000kg/m^3 = m/V; m = 4000kg/m^3 * V

pressure = (4000kg/m^3 * V * g)/A; volume/area = height; so, 1.2x10^6 = 4000kg/m^3 *g * h

The rest is all arithmetic, solve for h

Thanks!!!

 

[Raiden2012]

Oops sorry opejay, my mistake.
Look at Ibn for a better answer. I mistakenly thought it was a liquid.

 

[Opejay]

pressure = F/A = mg/A

Density = m/v; 4000kg/m^3 = m/V; m = 4000kg/m^3 * V

pressure = (4000kg/m^3 * V * g)/A; volume/area = height; so, 1.2x10^6 = 4000kg/m^3 *g * h

The rest is all arithmetic, solve for h

I'm kinda confused with this step " pressure = (4000* V * g ). What formula is that?

 

[Raiden2012]

Pressure = Force/Area
Force = mg where m = volume X density

 

[Opejay]

Pressure = Force/Area
Force = mg where m = volume X density

thanks!

 

[farnell]

Hey this is how I would have done it....

p = 4000 kg/ m^3 b/c density is 4 times that of water

Next, use P = Po + pgh

rearrange to P - Po = pgh

P- Po = guage pressure = 12 atm (given in problem that this is max pressure solid can withstand)

convert 12 atm to Pa and plug in values....

(12,00,000 Pa)= (4000 kg/m3) (10m/s2) (h)