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...
|
...
|
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Finding |
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apparent |
...
weight |
...
using |
...
normal |
...
force. |
...
One
...
way
...
that
...
we
...
perceive
...
weight
...
is
...
the
...
normal
...
force
...
we
...
experience
...
from
...
the
...
ground.
...
In
...
physics
...
problems,
...
when
...
you
...
are
...
asked
...
to
...
determine
...
apparent
...
weight,
...
the
...
quickest
...
method
...
is
...
usually
...
to
...
compute
...
the
...
normal
...
force
...
provided
...
by
...
the
...
"ground".
...
One
...
way
...
to
...
experience
...
a
...
reduced
...
apparent
...
weight
...
is
...
to
...
strap
...
into
...
a
...
harness
...
of
...
ropes
...
and
...
have
...
someone
...
(or
...
some
...
weight)
...
pull
...
down
...
on
...
the
...
other
...
end
...
like
...
they
...
do
...
in
...
theater
...
or
...
films.
...
Another
...
way
...
is
...
to
...
jump
...
into
...
a
...
swimming
...
pool,
...
where
...
the
...
water
...
lifts
...
up
...
on
...
you.
...
Another
...
possibility,
...
which
...
we
...
explore
...
in
...
this
...
problem,
...
is
...
to
...
enter
...
an
...
environment
...
where
...
the
...
"ground"
...
is
...
capable
...
of
...
moving,
...
such
...
as
...
an elevator.
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elevator.
h2. Part A
Suppose a person with a weight of 686 N is in an elevator which is descending at a constant rate of 1.0 m/s and speeding up at a rate of 3.0 m/s{color:black}^2^{color}. What is the person's apparent weight?
h4. Solution
*System:* Person as a [point particle].
*Interactions:* External influences from the earth (gravity) and the floor of the elevator (normal force).
*Model:* [Point Particle Dynamics].
*Approach:* The physical picture and free body diagram for the person is:
|!elevator1.png!|!elevator2.png!|
||Physical Picture||Free Body Diagram||
which leads to the form of [Newton's 2nd Law|Newton's Second Law] for the _y_ direction:
{latex}
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