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Grade 12th passMechanics

The height of a mercury barometer is 75 cm at sea level and 50 cm at the top of a hill. Ratio of density of mercury to that of air is 10^4. The height of the hill is

A) 250 m

B) 2.5 km

C) 1.25 km

D) 750 m

Profile image of Sahani Kumar
7 Years agoGrade 12th pass
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4 Answers

Profile image of Arun
7 Years ago
Dear student
 
I am getting my answer as 2500 m or 2.5 km
 
Hence option B is correct.
 
Regards
Arun (askIITians forum expert)
Profile image of Sahani Kumar
7 Years ago
Please explain me how you did it. Please plz........I want it's solution urgently. Sir I will be so much thankful to you. 
Profile image of Sarang
7 Years ago
Pressure difference between sea level and the hill would be
dP1 = dh1 X ρm X g  (1)
where dh = h1 (sea level mercury height = 75 cm) - h2 (hill top mercury height = 50 cm)
 ρm is the density of mercury
 
and  the pressure difference in atmospheric pressure would be
dP2 = dh2 X ρa X g  (2)
where dh2 is the height of the hill, ρa is the density of air 
now, we know that (1) = (2), so
 
dh1 X ρm X g = dh2 X ρa X g
 
by substituting appropriate values and rearranging, we get
 
dh2 = 0.25 X  (ρm/ ρa) = 0.25 X 104 m
or dh2 = 2500 m 
 
thus, the height of the hill is 
dh2 = 2500m = 2.5 km
 
Profile image of Sarang
7 Years ago
B is correct answer 
Correct option B 
Explanation in answer 1
Sorry for 2 answers ….
 
Regards....
Sarang