1
Lecture 15
More Interacting Bodies
Stephen D. Downing
Mechanical Science and Engineering
© 2001 - 2008 University of Illinois Board of Trustees, All Rights Reserved
TAM 210/211
Engineering Mechanics: Statics
TAM 210/211 - Lecture 15
© 2008 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved
1 of 15
Homework 4.106
Assume cable is
horizontal
Homework #5 is due on Fri Feb 22nd

This
** preview**
has intentionally

**sections.**

*blurred***to view the full version.**

*Sign up*
2
TAM 210/211 - Lecture 15
© 2008 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved
2 of 15
Interacting Bodies
Suppose we have the system
shown in (a) above. If we wish
to draw a FBD of the bar and
the pulley the result is shown
in B
Note: No forces are shown at B
between the pulley and the bar
because they are internal forces
(and would cancel anyway)
Here we have 3 forces, 3 unknowns so the solution does exist.
∑
∑
∑
=
⇒
=
=
⇒
=
=
⇒
=
N
320
A
0
F
N
160
A
0
F
N
200
T
0
M
Y
Y
X
X
A
If the body is in equilibrium, each of it’s parts is also in equilibrium
TAM 210/211 - Lecture 15
© 2008 Stephen Downing, University of Illinois at Urbana-Champaign, All Rights Reserved
3 of 15
Separate FBDs
Hence we can draw FBDs for beam AB and
the pulley at B separately as shown
We can write separate equilibrium
equations for (b) first to solve for T, P
X
, P
Y
Then use P
X
, P
Y
in (a) to solve for A
X
, A
Y
Note: in (a) there are initially 4 unknown
forces so we cannot begin with (a)