Can someone please help...

[Robotjim]

Hello I am having a hard time with this physics problem , if anyone would like to pitch in some ideas I would greatly appreciate it.. Thank you

a) Compute the mass of a 6.5 ft by 2.5 ft by 1.0 ft bathtub filled with water.

b)Compute the mass of the same bathtub filled with pennies. Assume the pennies are pure copper and fill 75% of the volume of the tub.

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[Isoprop]

a) they give you the volume of the water, so you need to convert volume to mass by knowing the density.
b) same approach. volume is equal to .75 times the volume calculated in (a). use density to convert volume to mass.

 

[Robotjim]

I know but they don't give me the density. I guess I am just supposed to look it up..

Anyway, once I have the density is it just m=dv?

 

[engineeredout]

Well for water you're supposed to know that the density is 1000kg/m^3 or 62.3lbm/ft^3. Doubt you need to know the density of copper, you sure thats not somewhere in the problem, or maybe the question before it?

And for the actual calculations, think about the units. If you have 500ft^3 as your volume, then you're going to want to multiply that by 62.3 lbm/ft^3 so that the f^3 cancels out and you're left with lbm.

 

[Vihsadas]

The above posters are right, but I wanted to comment that its weird that the question was asked with units of 'ft'. I seriously doubt the MCAT would ask in those units without giving you the conversion factor. They may, however, ask in units of meters and expect you to know the density of water.

 

[pingouin]

moved to MCAT Q/A