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InertialRef
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Homework Statement
a)Suppose the chancellor of the university drops a 2.00 kg water balloon from the administration
building balcony 10.0 m above the ground. The chancellor takes the origin of his vertical axis
to be even with the balcony. A student standing on the ground below the chancellor decides
she would rather have the origin of her coordinate system be the ground at her feet.
b)Calculate the value of the gravitational potential energy of the balloon before it is dropped and
just as it hits the ground for each of the frames of reference.
chancellor frame:
PE bef= (2.00)(9.81)(0 m) = 0 J
PE aft= (2.00)(9.81)(10 m) = 196.2 J
student frame:
PE bef= (2.00)(9.81)(10 m) = 196.2 J
PE aft= (2.00)(9.81)(0) = 0 J
c)Calculate the value of the kinetic energy of the balloon before it is dropped and just as it hits the ground for each of the frames of reference.
chancellor frame:
KE bef= (0.5)(2.00)(0)^2 = 0
KE aft= (0.5)(2.00)(9.81*(√(20/9.81)))^2 = -196.2
I calculated for the final velocity using the principle kinematics equation.
student frame:
KE bef= 0
KE aft= -196.2
d)Calculate the total mechanical energy of the balloon before it is dropped and just as it hits the ground for each of the frames of reference.
chancellor frame:
TME bef=
TME aft=
student frame:
TME bef=
TME aft=
Homework Equations
KE = (0.5)m(v^2)
PE = mgh
The Attempt at a Solution
I've solved for most of it, since it was pretty simple, but I'm stuck at part d. Shouldn't total mechanical energy always be conserved? How is it that for the president, total mechanical energy isn't conserved? The total energy initially = 0, then it increases. Why does it do that?
I understand that when looked at from one frame of reference only, the total energy is conserved. But when looked at from two frames of references, total energy only appears to not be conserved, but it actually is. Is there some way to correct for this, or is the only way to see if mechanical energy is conserved is to observe such motion from one frame of reference?