# Force necessary to support mass on Hydraulic Jack?

1. Aug 17, 2009

### jumpingjack90

Force necessary to support mass on Hydraulic Jack???

1. The problem statement, all variables and given/known data
Piston 1 in the figure has a diameter of 1.31 cm. distance of 2 in
Piston 2 has a diameter of 7.91 cm. distance of 10 in
In the absence of friction, determine the force F, necessary to support an object with a mass of 904 kg placed on piston 2. (Neglect the height difference between the bottom of the two pistons, and assume that the pistons are massless).

2. Relevant equations
F1*d1 = Fp*d2, where d1 is the moment arm of F1, and d2 is
the moment arm of Fp.

3. The attempt at a solution
Fp = (F1*d1)/d2
(904)(9.81)/(pi)(0.003955)^2= F/(pi)(0.00655)^2
F=242.98 N which was incorrect.
anyone have an idea of what I should do and what equation to use? Thanks!

2. Aug 17, 2009

### Redbelly98

Staff Emeritus
Re: Force necessary to support mass on Hydraulic Jack???

I think we'll need to see the figure before we can help you out.

3. Aug 17, 2009

### jumpingjack90

Re: Force necessary to support mass on Hydraulic Jack???

http://img6.imageshack.us/img6/7849/1808317ca439856447261f7.gif [Broken]

this is the link for the picture.

Last edited by a moderator: May 4, 2017
4. Aug 17, 2009

### djeitnstine

Re: Force necessary to support mass on Hydraulic Jack???

Neglecting the height difference means the pressure should be the same, thus $$F_1 A_1 = F_2 A_2$$

This is would be the force exerted on the small piston.

You should know how to find the force needed by the hand from this.

5. Aug 17, 2009

### Redbelly98

Staff Emeritus
Re: Force necessary to support mass on Hydraulic Jack???

You have correctly found F1, the force on the smaller piston. However, they are asking for Fp (labelled simply F in the figure), the force exerted by the hand.

You have the equation to find Fp given F1.

6. Aug 18, 2009

### jumpingjack90

Re: Force necessary to support mass on Hydraulic Jack???

ok. I used the equation given and solved for Fp. I had (242.98)(pi*(0.03955)^2))/(pi)*(0.00655)^2=Fp=8858.92 N, which is also incorrect.
what am I doing wrong?

7. Aug 18, 2009

### jumpingjack90

Re: Force necessary to support mass on Hydraulic Jack???

nvm. I solved it! thanks everyone for your input!

8. Mar 1, 2011

### george88b

Re: Force necessary to support mass on Hydraulic Jack???

how u solved it my friend?