ANSWER: The torque of the beam is mgl/2.
Hi, since you didn´t put the whole problem I will solve your questions with this one.
A 2.90 m-long, 390. kg steel beam extends horizontally from the point
where it has been bolted to the framework of a new building under
construction. A 71.0 kg construction worker stands at the far end of
the beam. What is the magnitude of the torque about the point where
the beam is bolted into place?
STEP-BY-STEP EXPLANATION:
The sum of the torque is T1+T2, and the person is standing at the
edge of the beam. I do know the torque of the person standing at the
edge, which is 2.90 m * 71.0 kg * 9.8 m/s2 = 2.02 x 103
N-m.
Your steel beam, assuming that it is uniform in mass, should have its
downward force exactly in the middle. Think of the steel beam as a
point particle, and all the mass is focused at its center. The product of
its weight and one-half its length will give you its torque. And the
person is standing at the edge at that distance, there is another
downward force there. Then sum up all the torques.
The torque of the beam is mgl/2.
