Unit 2 Class Notes

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Unit 2 Class Notes
The Kinematics Equations (1D Equations of Motion)

• Honors Physics

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Day 6
Mixed Review (part II)
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Dx 2,224.5m
ttotal m28.72 sec
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Clearly this is a free-fall problem
Remember the free-fall assumptions
V1 0, a -9.8m/s2, down is negative
Solve the appropriate equations
What must be neglected??? AIR RESISTANCE!!!
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Again, this is a free-fall problem
Remember the free-fall assumptions
V1 0, a -9.8m/s2, down is negative
Solve the appropriate equations
How far will it fall from 3-4 seconds?
During the 20th second?
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Clearly this is a throw up problem
Remember the assumptions
V2 0 (_at_ top), a -9.8m/s2, down is
negative
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Make sure to draw a picture and label the points
appropriately.
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What must be neglected??? AIR RESISTANCE!!!
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choose points 1 2
choose points 1 2
choose points 1 4
choose points 1 3
Clearly this is a throw up problem
Remember the assumptions
V2 0 (_at_ top), a -9.8m/s2, down is
negative
Make sure to draw a picture and label the points
appropriately.
Choose two points, and work between these two
points.
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Points 1-2
v1 10 m/s
a -9.8 m/s2
v2 0 m/s
Points 1-4
OR .
v1 10 m/s
a -9.8 m/s2
Simply double the time from point 1 to point 2.
Dx 0 m
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v1 10 m/s
a -9.8 m/s2
Dx 5m
Solve this quadratic equation for the times
Graph y -4.9x2 10x - 5
Hit 2nd Trace, ZERO
It is 5 meters above the ground on the way UP and
on the way DOWN.
Left Bound, Right Bound, Guess .
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Remember your assumptions, draw a picture, pick
your points.
Points 1-2
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This is a chase problem!!!
x2N x2O
But its also a CHALLENGING chase problem. Why?
Because the new car undergoes two different
motions (speeding up and then coasting).
Use the chase equation
Notice how each different motion needs to be
accounted for when writing the equation.
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Plug in what you know
How do we plug in for the times?
How do we find a?
tO t (the total time)
v1 0
taccel 40 sec (this was given)
v2 21 m/s
tcoast t 40 (the total time
minus the accel time)
t 40 sec
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Solve
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THE GRAPHICAL APPROACH!!!
When the areas under the curves are equal, the
new car has caught the older one.
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TONIGHTS HW
NONE ? ENJOY!!!
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