Calculate the torque due to the hinge.

Question

1. The drawbridge's weight: W = Mg = 6400 lb
2. Its length: ℓ = 40 ft
3. The height the cable reaches: h = 16 ft

I can't insert an image but the picture looks like this:

right triangle starting from 0.

1. 0 is the "hinge"
2. the y axis is meant to represent the drawbridge and goes to length L
3. the x axis is meant to be h
4. the hypotenuse of the right triangle is the cable of the bridge
5. the cable does not end at L, but instead ends at 3L/4 on the y axis

Answer 1

In static problems, the net torque is zero at all points for equilibrium. In order to solve problems, you do a force balance, vertically and horizontally (this will yield the forces up and sideways at the hinge). The third equation is a torque balance which is defined about the hinge (in order to have no torque contributions from the forces at the hinge - the lever arm is zero). This allows you to usually solve for the tension in the cable. (Once the tension is known, the force balances can be used).

The torque at the hinge is usually set to zero, so I do not understand the question.