# Homework Help: U-shaped manometer question(a tricky one)

1. Aug 30, 2010

### kushite

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

la u-shaped monometer has a cross section of 1cm^3, one side is closed, and the other other is open to the atmosphere, the barometer pressure is 1x10^5 pa. the manometer is filled with mercury, at a constant tempreture someone want to increase the pressure of the closed amount air to 3x10^5pa. what is the volume of the mercury to be added to the other open leg of the manometer? 9cm is given as the height of the air column at the closed leg.

2. Relevant equations

My problem is the answer doesnt match whatever i get, even if my reasoning is good

3. The attempt at a solution

because the pressure is to be increased at the air column, that column does not move, it remains at its height, so 1.2(air density)x9.8x0.09=atmospheric pressure+pressure due to the new height of the added mercury(h x 9.8x13600)

The should be the 'h'x the crossection. but the answer in my book is 162cm^3, i cant fo the life of understand why. PLEASE HELP