# Homework Help: Pressure questions!

1. Jan 24, 2006

### jkd989

A bodybuilder is holding a 35-kg steel barbell above her head. How much force would she have to exert if the barbell were lifted underwater?

In the hydraulic press used in a trash compactor, the radii of the input piston and the output plunger are 6.1 10-3 m and 4.5 10-2, respectively. If the height difference between the input piston and the output plunger can be neglected, what force is applied to the trash when the input force is 300 N?

Please answer these questions for me, they are the last two problems on my 100 problem worksheet that is due tomorrow. I have literally spent the past two hours trying to find the answers for these and i really need a good grade....Thanks in advance!!!

2. Jan 24, 2006

### jkd989

My problem for the first one is that i cant find any formulas or theories in my textbook that explain the situation. I answered the second problem what i think is correctly so please ignore that part.

3. Jan 25, 2006

### Staff: Mentor

Buoyancy: find the buoyancy of the barbell.

4. Jan 25, 2006

### jkd989

ok archimedes' principle states that the magnitude of buoyant force=weight of displaced fluid. But How can i have any idea what the weight of the displaced fluid is?

5. Jan 25, 2006

### jkd989

I also know that the mass density of steel is 7860 kg/m^3, while the mass density of water is 1000 kg/m^3

6. Jan 25, 2006

### jkd989

nevermind i solved it