Question

By sucking through a straw a boy can reduce the pressure in his lungs to 750 mm of Hg. (Density = 13.6 g/cm 3 ) using a straw he can drink water from a maximum depth of

Answer 1

Normal pressure is 760 mmHg so the boy can create a depression of 10 mmHg in his lungs.  

According to the law of floatation  

Weight of floating body = weight of displaced liquid  

wt. Of water displaced from glass = wt  of air of lung reduced (interm of mmHg) 

wt of water displaced from glass = density of water (d1) x volume of water displaced (v1) 

wt of air reduce from lung (interm of mmHg) = density of Hg(d2) x volume of air displaced (v2) 

Now d1 x v1 = d2 x v2 

And v1 = d2 x v2/d1 = 13.6 gcm –3 x10mm/ 1gcm –3 = 136mm = 13.6cm 

 

 

Density of water is 1gcm raise to power -3

Answer 2

Answer:

Ans. 13.6 cm

Explanation:

Pressure difference between lungs of student and atmosphere=760 - 750 = 10 mm of Hg

hdg = 10 mm of Hg = 1 cm of Hg

This pressure can only be used to drink water.

1 cm of Hg = pressure difference due to water column

=> 1 x 13.6 x g = h x 1 x g. [d of Hg=13.6 g/cm3]

=> 1 x 13.6 = h x 1

=> h = 13.6 cm

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