# Dentist Chair

1. Nov 26, 2007

### BuBbLeS01

1. The problem statement, all variables and given/known data
A dentist's chair of mass 207kg is supported by a hydraulic lift having a large piston of cross-sectional area 1403.0cm^2. The dentist has a foot pedal attached to a small piston of cross-sectional area 78.0cm^2. What force must be applied to the small piston to raise the chair.

2. Relevant equations
P=F/A
Fp/Ap = Fc/Ac

3. The attempt at a solution
Fp = Fc/Ac * Ap
Fp = 207kg/1403 * 78 = 112.78

- Why does Fp/Ap = Fc/Ac??
- Why is 207kg relate to 1403cm^2?
- What is the subscripts p and c???

2. Nov 26, 2007

### rock.freak667

Suggestion in your calculations when you said...
F=mg...so the force should be the weight..so you have to multiply by 9.81Nkg^-1 or whatever value you take as g and convert the cm^2 to m^2

"Why does Fp/Ap = Fc/Ac??"

Does this not mean that $P_p=P_c$ which just basically says that pressure is transmitted equally throughout a fluid...i.e. the pressure at one end is equal to the pressure at the other.

the subscripts p and c would be piston and chair respectively