Transcript Static Equilibrium: “The Hanging Sign Problem”

-Newton’s Laws Applications Equilibrium
Physics
Mrs. Coyle
Outline
• Solving Newton’s Laws Problems where the objects
are accelerating (involving tension, normal force).
• Static Equilibrium including the Suspended Sign,
Inclined Plane , Atwood Machine.
Example 1
• Two boxes are on a horizontal table. They are
connected by a string. Find the acceleration of
each box and the tension on the string, if a
force of 10N is applied horizontally.
M1 = 20kg
F=10N
M2= 5kg
Equilibrium: a)Static, b)Dynamic
∑F = 0
a=0
a) Static Equilibrium: the object is at rest, v=0.
b) Dynamic (Translational) Equilibrium: the
object is moving at constant velocity,
v=constant.
– The Equilibrant is a force that is exerted on the
system to bring it to equilibrium.
Suspended Sign Problem
How do you calculate the tensions in the strings?
-How do the angles affect the tensions?
Example 1
a)Calculate the tension in each string. The
mass of the sign is 2kg and the angles
formed between each string and the sign
are 300.
b)If the angles were 10o, what is the
tension and how does it compare with
the answer to a)?
Answer:
a) T1 = T2 = 20N
b) T1 = T2 = 58N
In which case is the tension greater?
http://wwwrcamnl.wr.usgs.gov/sws/SWTraining/cableways/design.htm
Do the angles affect the tension?
• Examples:
– Telephone or electrical wires.
– Picture frame wire.
Example 2
T1
T2
A sign is suspended as shown above.
Calculate the tension in each string.
Answer: T1 =289N, T2 =144N
Inclined Plane
Normal, N
Weight, mg
ө
Example 1- Find the acceleration.
F=35 N
m= 5kg
15°
Frictionless plane.
30o
Atwood Machine
• Express the
acceleration in terms
of m, M and g.
http://www.staff.amu.edu.pl/~romangoc/graphics/M3/7-atwood-machine/M3-7-fig1.gif
Find the acceleration and the tension
(assume frictionless surface).
M1
M2