Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

spring compression



Hi
I came across a problem in my physics class that I haven't been able to
resolve. Perhaps it is the result of mental overload, or failing memory
circuits. The problem is from University Physics by Young and Freedman,
Chapt 7, no. 60, the b part of the problem. The student is to calculate
how far a sping supported platform will compress if a 90 kg man steps
gently on it. I worked this by setting his weight (w=mg) equal to
Hooke's law force (F=kx) leading to x=mg/k. The instructors manual
worked the problem by setting the gravitational potential energy (U=mgx)
equal to the compressional energy (one-half k (x squared)) (sorry but I
don't know how to do superscripts with this program). This leads to the
expression x=2mg/k. What gives? Thanks for your help.