Register to reply 
Help in strain energy calculation 
Share this thread: 
#1
May1309, 11:03 PM

P: 10

1. The problem statement, all variables and given/known data
When a spring fixed at one end is pulled by a force of 8N, the extension is 40mm. Two such springs are joined in series and is pulled to produce a total extension of 40mm. What is the strain energy in the springs. 2. Relevant equations strain energy, U = Fe / 2 or U = F^{2}/2k *e is the extension while k is the spring constant. ( I found this equation online, correct me if this is wrong. ) 3. The attempt at a solution I calculate the strain energy of 1 spring first, which is 8 x 0.04m / 2 = 0.16J  for one spring, the spring constant should be F = ke 8 = 0.04k k = 200 For two spring, the spring constant is 1/k = 1/k_{1} + 1/k_{2} 1/k = 1/100 k = 100 hence, the force used to made an extension of 0.04m is F = 100 x 0.04 = 4N Thus, the strain energy is U = F^{2} / 2k = 16 / 200 = 0.08J or U = Fe /2 = 4 x 0.04 / 2 = 0.08J The answer provided by the book is 0.32J, which is differ with the answer I calculated, either one string or two strings. Can anyone correct the mistakes I made while doing calculation? Or the answer given is incorrect? 


#2
May1409, 07:49 AM

Sci Advisor
HW Helper
PF Gold
P: 2,532

Given the conditions you've described, the book answers seems to be incorrect.



Register to reply 
Related Discussions  
Strain energy at break for rubber  General Engineering  0  
Stress, Strain, Energy...  Introductory Physics Homework  6  
Strain energy for circular plates  Mechanical Engineering  11  
Strain energy  General Engineering  1  
Strain energy  Introductory Physics Homework  1 