One end of a heavy beam of mass M = 50.0 kg is hinged to a vertical wall, and the other end is tied to a steel cable of length 3.0 m, as shown in the figure. The other end of the cable is also attached to the wall at a distance of 4.0 m above the hinge. A mass m = 20.0 kg is hung from one end of the beam by a rope.
a) Determine the tensions in the cable and the rope,
b) Find the force the hinge exerts on the beam.

THINK:
(a) Determine the tension in the cable and rope.
(b) Find the forces the hinge exerts on the beam.
SKETCH:
The represented free body diagram as below:
RESEARCH:
When beam is at equilibrium,
The net torque on it is zero, therefore
…… (1)
The total force along
direction and
direction is zero due no motion.
Therefore 
SIMPLIFY:
From the sketch,
and length of the beam is 
Use hinge as a pivot point. From the equation (1), we have

Therefore the tension in the cable is

…… (2)
Here the tension in the rope is
…… (3)
(b)
Since the horizontal and vertical force are
,
From the figure,
The force the hinge exerts on the beam is 
…… (4)
Given data:
Mass of the beam is 
Length of the steel cable is 
The other end of the cable is attached to the wall at a distance above the hinge is

Mass of the hinging object is 
CALCULATE:
(a)
The tension in the rope is

From the figure , the angle:

By substituting all known values in the equation (2), we get the tension in the cable.

(b)
By substituting all known values in the equation (4), we get the force the hinge exerts on the beam.
