Work Done by Spring

  • Thread starter McAfee
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  • #1
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Homework Statement



A spring with a spring constant of 10 N/cm has a cage attached to one end (Fig. 7-53). Taking rightward as the positive direction, (a) how much work does the spring force do on the cage when the spring is stretched from its relaxed length by 7.6 mm? (b) How much additional work is done by the spring force when the spring is stretched by an additional 7.6 mm?

DP8KM.jpg

Homework Equations



W= -(½)*k*(d)^2


The Attempt at a Solution


First, I changed the units.
d=.0076m
k=1000 N/m

For

a) W = ½*1000*x0.0076² = 0.02888 J


b) W = ½*1000*(0.0152² - 0.0076²) = 0.08664 J

I know that I did the right work but I am still wrong. Does the answer have to be negative? But the problem states that the right is positive. I can't find my mistake.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
96
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any help?
 
  • #3
PeterO
Homework Helper
2,425
47

Homework Statement



A spring with a spring constant of 10 N/cm has a cage attached to one end (Fig. 7-53). Taking rightward as the positive direction, (a) how much work does the spring force do on the cage when the spring is stretched from its relaxed length by 7.6 mm? (b) How much additional work is done by the spring force when the spring is stretched by an additional 7.6 mm?

DP8KM.jpg

Homework Equations



W= -(½)*k*(d)^2


The Attempt at a Solution


First, I changed the units.
d=.0076m
k=1000 N/m

For

a) W = ½*1000*x0.0076² = 0.02888 J


b) W = ½*1000*(0.0152² - 0.0076²) = 0.08664 J

I know that I did the right work but I am still wrong. Does the answer have to be negative? But the problem states that the right is positive. I can't find my mistake.

Homework Statement





Homework Equations





The Attempt at a Solution

While stretching the spring to the right, you have done a positive amount of work. All that time the spring has been pulling to the left, so the spring force has been doing negative work.
 
  • #4
96
0
While stretching the spring to the right, you have done a positive amount of work. All that time the spring has been pulling to the left, so the spring force has been doing negative work.
Thanks alot for helping making this clear for me.
 

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