Sec 3 Physics Question

kkhing SG

Please help me with this Physics question:

Air is made up of about 80% nitrogen and 20% oxygen by volume. The densities of air and oxygen are 1.29 kg/m3 and 1.43/m3 respectively. What is the density of nitrogen?

Thanks.

eagle SG

Density = mass / volume

mass = density * volume

Let vol of air = V, hence vol of nitrogen = 0.8V and vol of oxygen = 0.2V

mass of air = mass of nitrogen + mass of oxygen
density of air * V = density of nitrogen * 0.8V + density of oxygen * 0.2V

You should be able to solve from here :)

Samdol1978 SG

Any kind bros might be able to help me with this thermodynamic question?

1)If on average in the systemic circulation loop,the flow rate through the body is 10^-4 m3/s with a supply pressure from the heart at 100mmHG and return pressure at 15mmHG,what is the rate at which work is done by the heart iin circulating the blood?Assume neglible changes in flow area and flow velocity between supply and return openings.(Note:1mmHG=133.3PA)

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My workings so far

Flow rate=Volume flow rate

Q=(P1-P2)(Pie*R^4)/(8nL) whereby n=Viscocity of blood,L=Length of tubing,R=Radius of tubing

Heart Pressure Out=100mmHG=100*133=13300 Pa=13300 N/m2

Heart Pressure In=15mmgHG=15*133=1995 Pa=1995 N/m2

Pressure Difference=13300 Pa=13300 N/m2