Math 151, Workshop 8
1.
A flagpole is 40 feet high and stands on level ground. A
flag is attached to a 120 foot rope passing through a pulley
at the top of the flagpole. The other end of the rope is tied
to a car at ground level. If the car is driving directly away
from the flagpole at 3 ft/sec, how fast is the flag rising
when the top of the flag is 20 feet off the ground?
R
r
2.
Two circles have the same center.
The inner circle has radius
r
which is increasing at the rate of 3 inches per second. The outer
circle has radius
R
which is increasing at the rate of 2 inches per
second. Suppose that
A
is the area of the region
between
the circles.
At a certain time,
r
is 7 inches and
R
is 10 inches.
What is
A
at
that time? How fast is
A
changing at that time? Is
A
increasing or
decreasing at that time?
3.
The numbers
R
1
,
R
2
,
R
3
, and
R
satisfy the following equation:
1
R
1
+
1
R
2
+
1
R
3
=
1
R
.
(The total resistance
R
, of a circuit composed of parallel resistances
R
1
,
R
2
, and
R
3
.)
a) If
R
1
= 1 and
R
2
= 2 and
R
3
= 3, compute
R
exactly.
b) If both
R
1
and
R
3
are held constant, and
R
2
is increased by
.
05, what is the approximate
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 Spring '08
 Madey
 Physics, Numerical Analysis, Approximation, Work, approximate change, parallel resistances R1

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