HW#5a
Page 1 of 4
For circular motion, we know that the total force in the radius direction pointing to the center equals
to ma
cp.
All we need to do is to
find all the forces at that position
, add them in radius direction and
solve the equation.
.We should use v at that position too.
Applies to all problems.
1,
Ch. 6 Prob #46 - circ motion centrifuge
To test the effects of high acceleration on the human body, NASA has constructed a large centrifuge
at the Manned Spacecraft Center in Houston. In this device, astronauts are placed in a capsule that
moves in a circular path of radius 15 m. If the astronauts in this centrifuge experience a centripetal
acceleration
9
times that of gravity (or "
9
g's"), what must be the speed of the capsule?
2, Jill of the Jungle swings on a vine
6.5
m long. What is the tension in the vine if Jill, whose mass is
61 kg, is moving at
2.4
m/s when the vine is vertical?
3.
Driving in your car with a constant speed of 12 m/s, you encounter a bump in the road that has a circular
cross section, as indicated in Figure 6-35. If the radius of curvature of the bump is
r
= 35 m, find the apparent
weight of a
67
kg person in your car as you pass over the top of the bump.
Attention that a
cp
and the net force is pointing to center. Also the unit is kN, not N.
Normal force is less than
mg, the total acceleration is downward. That’s how the car “falls” (changes direction) after the bump.

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