Calculating Work Needed to Change Spring Length

In summary, to find the work required to change the length of a spring from 10 cm to 14 cm given a stiffness of 50 N/m, you can use the formula W = 0.5K(s2 - s1), where K is the stiffness and s2 and s1 are the stretched lengths of the spring. This would result in a work value of 0.08 J. Alternatively, you can integrate the force over the distance, or calculate the potential energy at each length and find the difference.
  • #1
mshah3
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Homework Statement



A spring has a relaxed length of 5 cm and a stiffness of 50 N/m. How much work must you do to change its length from 10 cm to 14 cm?


Homework Equations



W= -U = F(delta R) = (Ks)(s)


The Attempt at a Solution




-attempted solving this problem using the formula above
-got a value of 0.08 J
-value is apparently incorrect
-not quite sure where I went wrong
 
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  • #2
The spring force is not constant, so you can't just use W = Fx. You'll have to integrate the force over the distance.

Alternatively, you can use the formula for the potential energy stored in a stretched spring.
 
  • #3
so is the formula (0.5) K s^2 ?

K=stiffness = 50
s= 14-10 = 4

is this an accurate calculation?
 
  • #4
The formula is correct but your use of it is not. In the formula, s stands for the amount of stretch beyond the unstretched length.

When the spring has length 10, how much is it stretched?
When the spring has length 14, how much is it stretched?

Compare the energy at each of those positions.
 
  • #5
oh ok... I think I understand

so essentially, I should use that formula separately to find work at 10cm (s=5) and 14cm(s=9)

and then find the difference of the too work values?
 
  • #6
That's correct.
 

1. How do you calculate the work needed to change the length of a spring?

The work needed to change the length of a spring can be calculated using the formula W = 0.5 * k * (x^2 - x0^2), where W is the work, k is the spring constant, x is the final length of the spring, and x0 is the initial length of the spring.

2. What is the spring constant and how does it affect the calculation of work needed?

The spring constant is a measure of how stiff a spring is. It is represented by the letter k and is measured in units of force per distance, such as N/m. The larger the spring constant, the more work will be needed to change the length of the spring.

3. Can you provide an example of calculating work needed to change spring length?

For example, let's say a spring with a spring constant of 10 N/m has an initial length of 0.5 m and is compressed to a final length of 0.2 m. The work needed to change the spring length would be calculated as follows: W = 0.5 * 10 N/m * ((0.2 m)^2 - (0.5 m)^2) = 0.9 J. Therefore, 0.9 Joules of work would be needed to compress the spring from 0.5 m to 0.2 m.

4. Is the work needed to change spring length always positive?

No, the work needed to change spring length can be either positive or negative depending on the direction of the force applied to the spring. If the force is in the same direction as the displacement, the work will be positive. But if the force is in the opposite direction of the displacement, the work will be negative.

5. What are some real-world applications of calculating work needed to change spring length?

The calculation of work needed to change spring length is important in various fields, including engineering, physics, and mechanics. It is commonly used in designing and testing springs for different applications, such as in shock absorbers, car suspensions, and door hinges. It is also used to determine the energy stored in a spring, which is crucial in designing efficient and safe structures.

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