# Homework Help: Oil manometer

1. Nov 15, 2009

1. The problem statement, all variables and given/known data

A manometer using oil (density 0.91 g/cm3) as a fluid is connected to an air tank. Suddenly the pressure in the tank increases by 0.72 cm of Hg. (a) By how much does the fluid level rise in the side of the manometer that is open to the atmosphere? (b) What would your answer be if the manometer used mercury instead?

2. Relevant equations

P = rho*gravity*height

3. The attempt at a solution
I have looked at several options of solving this problem. None of them make any sense to me. Please help. Thankyou!!

2. Nov 15, 2009

### mgb_phys

The question is asking how high does a column of oil have to be to weigh the same as a 0.72cm column of mercury

3. Nov 16, 2009

ok.
so i set the to two pressures equal to each other
so i got P(oil)=P(mercury)
(.91)(980)h = (980)(.72)(13.6)
solved for h, and provided my answer in cm but its not right :\

4. Nov 16, 2009

### mgb_phys

If i'm reaing the question in the same way as you that should be correct (you can ignore 'g' it cancels)
The oil is roughly 15x less dense than mercury - so you should have an answer around 10cm (roughly)

5. Nov 16, 2009