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Solve: (a)
The food energy equals
so
(b)
The mechanical energy would be 20% of the results of part (a):
7.40. Set Up:
Set 20% of the food energy (in joules) equal to the total work you do in raising the weight
N
times.
Solve:
For each arm raise, you do work equal to
where
Reflect:
It is not reasonable to do this many repetitions in a single exercise session.
7.41. Set Up:
Set 20% of the food energy (in joules) equal to the total work you do in jumping upward a distance
of
N
times.
Solve:
The total time it would take is thus
Reflect:
This would be a very strenuous workout even for a very fit person.
7.42. Set Up:
Use
Setting
and
gives
Solve:
7.43 Set Up:
For part (a),
Take
and
For part (b), use
with
and
this gives
Solve: (a)
(b)
The final kinetic energy of each kilogram is equal to the initial potential energy,
while
the corresponding speed is
By comparison, for a 70 kg person,
(c)
To double
double
since
mg
is constant, this means
h
must be doubled. You therefore need
To
double
you must increase
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 Spring '07
 Shoberg
 Energy, Work

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