by moonbase
 P: 21 1. The problem statement, all variables and given/known data A cart of mass m = 3 kg carrying a spring of spring constant k = 46 N/m and moving at speed v = 2.8 m/s hits a stationary cart of mass M = 8 kg. Assume all motion is along a line. What is the maximum amount the spring will be compressed? 2. Relevant equations PEspring=0.5kx2 KEinitial=0.5mv2 3. The attempt at a solution A previous part of this question asked me to calculate the mechanical energy in the center of mass frame, which I correctly found to be 8.55 J. I then had to find the total potential energy of the system when the spring is fully compressed, which I correctly calculated to also be 8.55 J. But when I plug this into the spring energy equation, the value I get for x is apparently incorrect. 0.5(46)x2=8.55 -> x=0.61 I must be missing a step here. Anyone see what I did wrong?
HW Helper
P: 2,315
 Quote by moonbase 1. The problem statement, all variables and given/known data A cart of mass m = 3 kg carrying a spring of spring constant k = 46 N/m and moving at speed v = 2.8 m/s hits a stationary cart of mass M = 8 kg. Assume all motion is along a line. What is the maximum amount the spring will be compressed? 2. Relevant equations PEspring=0.5kx2 KEinitial=0.5mv2 3. The attempt at a solution A previous part of this question asked me to calculate the mechanical energy in the center of mass frame, which I correctly found to be 8.55 J. I then had to find the total potential energy of the system when the spring is fully compressed, which I correctly calculated to also be 8.55 J. But when I plug this into the spring energy equation, the value I get for x is apparently incorrect. 0.5(46)x2=8.55 -> x=0.61 I must be missing a step here. Anyone see what I did wrong?
By my calculation, there was only about 7.15 J of energy stored in the spring? I may have been wrong - I did not have access to a calculator and couldn't be bothered using excel.
 P: 21 The program doesn't tell me how far off I am, but it told me that 8.55 in indeed correct for the spring's energy. Though when I inquire about it, it says "Look at this in the center of mass frame and consider how there is 8.55 J of mechanical energy. What does this say about the velocity of the carts in the center of mass frame when the spring is fully compressed?" I can't seem to find the problem, I tested it and know it's not a sig fig issue.
HW Helper
P: 2,315