PHYS 151 Spring 2017
Alyssa Tsenter
Supplemental Instruction
[email protected]
http://www.usc.edu/si
Midterm 2 Exam Review
A brief review of the material:
Centripetal Forces:
If there is a force causing UCM, then:
࠵?
= ࠵?࠵?
becomes
࠵?
%
=
&’
(
)
= ࠵?࠵?
+
࠵?
Note:
F
c
does not appear on the FBD! It is not a new type of force.
It is the form of Newton’s
2
nd
Law for UCM.
Work and Energy:
Whether a system is isolated or nonisolated we can write:
∆࠵?
/0/12&
= Σ࠵?
where T can be expanded as W + Q + …
Work has units of N*m, which is equal to a Joule (the unit for energy!) Work is defined as:
࠵? = ࠵? ∙ ∆࠵?
= ࠵?
∆࠵?
cos(࠵?)
*
*for a constant force
Using the force of a spring, which is
, we get that the work done by a spring is
.
WorkEnergy Theorem
࠵? = ࠵?
?
− ࠵?
A
=
1
2
࠵?࠵?
?
+
−
1
2
࠵?࠵?
A
+
࠵? = −∆࠵?
Potential energy
…in a gravitational field:
࠵? = ࠵?࠵?ℎ
…of a spring:
࠵? =
H
+
࠵?࠵?
+
Initial and final mechanical energies of an isolated system are
.
Power is the rate of energy transfer and has units of
:
࠵? =
࠵?
∆࠵?
Conservation of Energy
࠵?
A
+ ࠵?
A
= ࠵?
?
+ ࠵?
?
Can only use conservation of energy if there are no
.
Momentum:
Momentum is defined as:
࠵?
= ࠵?࠵?
To change the
p
of an object, need to apply a
.
This value is defined as:
࠵?
=
࠵?
࠵?࠵?
1
Q
1
R
= Δ࠵?
1T1
For a
system, the total momentum remains constant.
There are two types of collisions: Elastic and Inelastic
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PHYS 151 Spring 2017
Alyssa Tsenter
Supplemental Instruction
[email protected]
http://www.usc.edu/si
In an elastic collision,
is conserved.
In an inelastic collision,
is conserved.
o
For completely inelastic collisions, the two objects stick together after the collision
o
An explosion is a totally inelastic collision in reverse.
Approaching collision problems:
1.
Determine whether the collision is elastic or inelastic.
2.
Write down conservation of momentum equation (since this holds for both kinds of
collisions).
3.
Determine which terms are zero and then solve for unknowns.
Center of Mass:
The center of mass of a system of particles is the point at which the system’s whole mass can be
considered to be concentrated for the purpose of calculations.
The equation for finding the CM
is:
࠵?
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 Spring '07
 Katz
 Thermodynamics, mechanics, Force

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