Tutorial 2
MECH 101
Liang Tengfei
tfliang@ust.hk
Office phone : 2358-8811
Mobile : 6497-0191
Office hour : 14:00-15:00 Fri
1
General Equilibrium Problems
Equilibrium Conditions:
F  0
M  0
F  0
F  0
M  0
x
2D:
y
z
Today we will focus on:
How to select the free body?
How to draw the free body diagram?
How to build up equations?
3D:
F
F
F
x
0
y
0
z
0
M
M
M
x
0
y
0
z
0
Example 1
Determine the reactions at point A and B
 Isolate the free body &
 use reactions to replace the connections.
 Set up equations (resolve, sum)
A
Example 2
 Draw Free Body Diagram
(access: # unknow=# equation)
Answer:
Ay=183N
Ex=0, Ey=417N, ME=-500N.m
Example 3
The wall crane supports a
load of 3.5KN. Determine
the horizontal and vertical
components of the reaction
at pins A and D. Also, what is
the force in the cable at the
winch W? The jib ABC has a
weight of 500N and member
BD has a weight of 200N.
Each member is uniform and
has a center of gravity at its
center.
Answer:
pulley E: T=1.75KN
Member ABC :Ay=35KN
Ax=9.966KN
Member DB : Dx=9.116KN Dy=9.216KN
C
E
3.5KN
Extra question
If A and D are not in the same vertical line,
how can we solve this problem?