1
HW 5 Tips;
PHY 131 Sect. 10, 11, 15; Fall 2010
Prof. Pascuzzi
HW 5 covers Chapters 5 and 6; Uniform Circular motion & Newton
’
s Law of Gravitation
Information you may need;
Important steps in solving Uniform Circular Motion problems;
1)
Remember that even though the object is moving with constant
speed
, it is moving with
a
changing velocity
, because the velocity vector (tangent to the circle at any point) is
always pointing in a different direction.
Therefore, an object moving in uniform
circular motion is actually
accelerating
because its velocity (not speed) changes!
2)
Make your FBD.
3)
Apply
making sure that you remember that
toward the center of the
circle is POSITIVE and away from it is NEGATIVE
for your force vectors.
(Don
’
t
forget that
“
centripetal
”
means
“
TO THE CENTER, or
“
CENTER SEEKING
”
).
4)
WRITE OUT AND SUM THE FORCES , KEEPING YOUR SIGNS
STRAIGHT
…
then solve for any requested variables.
5)
A famous type of question is when something travels fast over a circular hill
…
.how fast
can it go before it leaves the ground?
The HINT is that it leaves the ground when the
normal force
N
becomes zero (see question first below).
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 Fall '03
 Rijssenbeek
 Circular Motion, Force, Mass, Normal Force, FBD

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