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course Phy 121
What are its final velocity in the vertical direction and its average velocity in the horizontal direction?
answer/question/discussion:
vertical final velocity:
ds=.122m
a=9.8m/s^2
v0=0m/s
vf^2=v0^2+2*a*ds
vf=sqrt(0m/s^2)+2*-9.8m/s^2*.122m
vf=-1.55m/s
dt=(vf+v0)/a
dt=(1.55m/s+0m/s)/9.8m/s^2
dt=.16s
Average Horizontal Velocity:
ds=40cm
dt=.16s
a=0m/s^2
ds=v0*dt+.5(a)(dt^2)
.04m=v0*.16s+.5*0m/s^2*(.16s)^2
v0=.25m/s
since the ball has zero acceleration, the initial velocity is the same as the average velocity
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Assuming zero acceleration in the horizontal direction, what are the vertical and horizontal components of its velocity the instant before striking the floor?
answer/question/discussion:
Vertical Component:-1.55m/s
Horizontal Component:.25m/s
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What are its speed and direction of motion at this instant?
answer/question/discussion:
Speed= sqrt((1.55m/s)^2+(.25m/s)^2)
Speed=1.57m/s
direction of motion:
arctan((-1.55m/s)/(.25m/s))=-80.84
80.84+360= 279 degrees
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What is its kinetic energy at this instant?
answer/question/discussion:
F=M*a
F=.07kg*9.8m/s^2
F=.686N
KE=F*ds
KE=.686N*.128m
KE=.087J
@&
`dKE = F * `ds, but the initial KE is not zero, so this doesn't give you the KE.
Your result is thus for `dKE, and this will be useful on a subsequent question.
For the present question, note that you just figured out the speed, which along with the mass is sufficient to get the KE.
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What was its kinetic energy as it left the tabletop?
answer/question/discussion:
F=M*a
F=.07kg*9.8m/s^2=.686N
F*ds=KE
.686N*0m=0J
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The object was moving as it left the tabletop, so its KE wasn't zero.
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What is the change in its gravitational potential energy from the tabletop to the floor?
answer/question/discussion:
PE_top=.086J
PE_bottom= 0J
Change in PE= .086J
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How are the the initial KE, the final KE and the change in PE related?
answer/question/discussion:
The difference between the final KE and the initial KE are the same as the change in PE
#$&*
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This should be the case, but you'll need to refigure some of your results to verify it.
You shouldn't find it difficult to do so.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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How much of the final KE is in the horizontal direction and how much in the vertical?
answer/question/discussion:
It is all in the vertical direction since the horizontal motion has zero acceleration.
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An object doesn't need to be accelerating to have a velocity. It usually does need to have accelerated at some point, but an object moving with nonzero speed and zero acceleration definitely has a kinetic energy.
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