Physics 2211: Lecture 6

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Physics 2211 Lecture 6

• 1-D motion Constant Acceleration Examples
• Free Fall
• Inclined Planes

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Free Fall
Constant acceleration due to gravity
y
t
v
t
y
a
t
a ? g
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1D MOTION ON AN INCLINED PLANE
A block slides (up or down) a frictionless ramp
that makes angle ? with respect to the
horizontal. How do we analyze the motion ?
Choose a convenient coordinate system
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Acceleration is due to gravity, constrained by
the presence of the inclined plane
Experiment shows that
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MOTION ON AN INCLINED PLANE
x
t
v
t
a
Labels and algebraic signs depend on your choice
of coordinate system!
t
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Move and invert coordinate system
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MOTION ON AN INCLINED
PLANE roles of coordinate system and initial
conditions are crucial
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• When throwing a ball straight up, which of the
  following is true about its velocity v and its
  acceleration a at the highest point in its path?
• (1) Both v 0 and a 0.
• (2) v ? 0, but a 0.
• (3) v 0, but a ? 0.

A block slides up an inclined plane and then back
down.
Which is the correct acceleration graph?
y
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1
5
2
3
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Problem-Solving Strategy constant
acceleration Model Use the particle
model. Visualize Use different
representations Pictorial representation,
physical representation (Motion diagrams),
graphical representation as appropriate. Go back
and forth between these three representations
they need not be done in any particular
order. Solve Only after modeling and visualizing
are complete is it time to develop a mathematical
representation ---here the kinematic equations
for constant acceleration come into play.
Assess Is your result believable? Does it have
proper units? Does it make physical sense?  
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• Santa loses his footing and slides down a snowy
  roof that is
• tilted at 27 degrees. If Santa slides 8 m
  before reaching the
• roofs edge, what is his speed at the instant
  he leaves the roof?

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• A rocket, initially at rest, accelerates straight
  upward from rest
• with constant acceleration a. The rocket runs
  out of fuel
• seconds after launch. Find the maximum height
  of the rocket.

check a -g
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Recap
1D Motion Constant Acceleration Free
Fall Motion on an Inclined Plane
Next Lecture
Finish Chapter 2 of Knight