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MASSACHUSETTS INSTITUTE OF TECHNOLOGY
Department of Physics
Physics 8.01T
Fall Term 2004
Problem Set 3: Newton's Laws of Motion, Motion: Force, Mass, and Acceleration, Vectors
in Physics Solutions
Problem 1: (
Relative Inertial Frames)
You and a friend are in an elevator that is rising at constant but unknown velocity
v
0
. You are
curious to know what speed the elevator is moving. You each happen to be carrying altimeters.
You get an idea and drop your keys from a height
h
above the floor of the elevator. You hold
one altimeter at the point where you dropped the keys and your friend places the other one on the
floor. You check your altimeter when you release the keys and find the keys are a height
d
above sea level. Your friend checks the other altimeter when the keys hit the floor and finds the
keys are the same height
d
above sea level. Assume that the gravitational constant is
g
. You
will analyze this problem from two different reference frames. The first reference frame moves
with the elevator. The second reference frame is fixed to the ground.
a)
As seen from a reference frame moving with elevator, how long does it take for the keys
to hit the floor?
b)
As seen from a reference frame fixed to the ground, using your result from part a), find
an expression for the speed of the elevator in terms of the height
h
.
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 Spring '10
 SPURLOCK
 Physics, Acceleration, Force, Inertia, Mass

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