Force necessary to support mass on Hydraulic Jack?

[jumpingjack90]

Force necessary to support mass on Hydraulic Jack?

Homework Statement

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).

Homework Equations

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

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!

 

[Redbelly98]

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

 

[jumpingjack90]

http://img6.imageshack.us/img6/7849/1808317ca439856447261f7.gif

this is the link for the picture.

 

[djeitnstine]

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.

 

[Redbelly98]

Homework Equations

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

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!

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.

 

[jumpingjack90]

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?

 

[jumpingjack90]

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

 

[george88b]

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

how u solved it my friend?