Length of bar needed to lift a crate(Torque, static equilibrium problem)

[Raziel2701]

Homework Statement

A large crate weighing 4520 N rests on four 12-cm-high blocks on a horizontal surface (figure below). The crate is 2.0 m long, 1.2 m high, and 1.2 m deep. You are asked to lift one end of the crate using a long steel pry bar. The fulcrum on the pry bar is 11 cm from the end that lifts the crate. Estimate the length of the bar you will need to lift the end of the crate. (Assume the maximum force you can apply is 500 N and that the pry bar is massless. Also assume that the bend I am the pry bar is negligible.)

Here's a picture of the setup: http://imgur.com/DtZh2

The Attempt at a Solution

Sum of forces on crate about y direction:

-4520 + N = 0

Sum of torques should be zero. My question is , what forces are exerting torques? So if I push down on the prybar, I push up on the crate, so my pushing down on the prybar exerts a torque on the bar along its length right?

So I have FL being one torque, where F is my 500N and L is the length of the prybar I wish to solve for.

So what else would be exerting torque? Because so far I have the sum of forces in the y direction, the one torque from my applied force but that's not enough.

 

[tiny-tim]

Hi Raziel2701!

The forces on the pry bar are the 500N at one end, the https://www.physicsforums.com/library.php?do=view_item&itemid=73" from the crate at the other end, and the reaction force from the ground.