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# Physics/Work , energy and power

Question
Sir,
"An overhead water tank is fixed at the height of 10m from thground and has a capacity of 500l. Calculate the time required to fill the tank from a pump of 0.5 H.P.  whose efficiency is 90%"
I understand that first we have to find power in watt which is probably equal to 373 watt. But what about the volume?? How to get mass so that I can use it in the relation W=m*g*h. Please help me out.

Hello,

For these types of problems, the key is to know the liquid type.  In your case, it is probably water.  Once you know what is being pumped, you can use the density to get the mass.  Water has a density of 1.0 g/mL (or 1 kg/L). So, for this problem the mass you need to move is 500 L * 1 kg/L, or 500 kg.

Other problems may have you pumping something else.  In that case, you will need to get the density from someplace.  There are many online tables that have liquid densities.  These will be in units of g/mL or kg/L.  Sometimes density will be called "specific gravity" and be listed in kg/cubic meter (kg/m^3).

I hope this helps!

Best regards,
Jeff
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Physics

Volunteer

#### Dr. Jeffery Raymond

##### Expertise

Materials chemistry. Materials science. Spectroscopy. Polymer science. Physical Chemistry. General Physics. Technical writing. General Applied Mathematics. Nanomaterials. Optoelectronic Behavior. Science Policy.

##### Experience

Teaching: General Inorganic Chemistry I & II, Organic Chemistry I & II, Physical Chemistry I, Polymeric Materials, General Physics I, Calculus I & II
My prior experience includes the United States Army and three years as a development chemist in industry. Currently I am the Assistant Director of the Laboratory for Synthetic Biological Interactions. All told, 13 years of experience in research, development and science education.

Organizations
Texas A&M University, American Chemical Society, POLY-ACS, SPIE

Publications
Journal of the American Chemical Society, Nanoletters, Journal of Physical Chemistry C, Journal of Physical Chemistry Letters, Ultramicroscopy Proceedings of SPIE, Proceedings of MRS, Polymer News, Chemical and Engineering News, Nano Letters, Small, Chemistry.org, Angewandte

Education/Credentials
PhD Macromolecular Science and Engineering (Photophysics/Nanomaterials Concentration), MS Materials Science, BS Chemistry and Physics, Graduate Certificate in Science Policy, AAS Chemical Technology, AAS Engineering Technology