Torque rock problem

  • #1

Homework Statement


Someone places a 6.0m long steel rod on a rock so that one end is under a baby moose weighing 2.0 kN. THe person pushes down on the other end of the rod with a force of 400N, and the moose is held in the air at rest. The rock was:
(a) 1.0m from the moose
(b) 5.0m from the moose
(c) 1.0m from the person
(d) 6.0m from the person
(e) none of these


Homework Equations


T = Fl
Tnet = 0
Fnet = 0

The Attempt at a Solution



So I began this problem by drawing a free body diagram. I drew the 2000N moose on the right end of a rod that is balanced in the center by a rock. I drew that there are two forces acting in the downward direction, the 400N force and the 2000N W. Since I don't know the force applied on the rod by the rock, I made the center of gravity my axis of rotation. My teacher gave us the answers at the end of class, and said that the answer is (a). Is this because of the ratio between the forces of the moose and the person? How do you know that there's a relationship between the force applied and the location to which it's applied? Thanks in advance.
 

Answers and Replies

  • #2
berkeman
Mentor
57,676
7,698
The torques are summed about the fulcrum for a lever. The rock is the fulcrum in this example.
 

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