Page 44 - eEISBN FINALIZE

ii. Show All Forces

Show on this sketch all the forces acting on the particle. There are two class of
forces that act on the particle. They can be active forces, which tend to set the particle

in motion, or they can be reactive forces which are the results of the constraints or
supports that tend to prevent motion.

iii. Identify Each Force

The forces that are known should be labeled complete with their magnitudes and

directions. Letters are used to represent the magnitudes and directions of forces that

are not known.

Example 1

The sack A shown in figure below has a weight of 20 N.determine the weight of the sack at
B and the force in each cord needed to hold the system in equillibrium

G

30
0
D
E

3 5
4
C 45 0

20N

Solution
B

FEG

E 60 0

45 0

20N
FEC

Resolving each force into x and y component using trigonometry we have

35