# Homework Help: Initial Tension Of Parallel Spring System

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1. Mar 23, 2015

### stannard97

1. The problem statement, all variables and given/known data
How to calculate initial tension or pretension in a system of two parallel springs.
F=5.33213N
K1+K2=53.0597
x=0.095

Individual springs have initial tension of 0.25N so I would expect an answer of 0.5N but I can't get there.

2. Relevant equations
F=(k1+k2)x

3. The attempt at a solution
Total force applied - Initial tension = (k1+k2)x
Total force applied - (k1+k2)x = Initial tension = 0.29?

2. Mar 23, 2015

### AlephNumbers

Could you please restate the problem exactly as it reads? And provide a drawing perhaps? Also, I have never seen the word pretension used that way. Ever.

3. Mar 23, 2015

### AlephNumbers

Those pretentious springs! Such over-inflated senses of self-worth!

4. Mar 23, 2015

### stannard97

Calculate the initial tension of two springs in parallel by treating them as a single spring. Initial tension as in the force needed to begin extending the spring. Ktotal is the sum of individual spring constants and total force is shared between both springs.

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5. Mar 23, 2015

### AlephNumbers

I would say that (k1 + k2)x - F = initial spring tension, not F - (k1 + k2)x.

6. Mar 23, 2015

### AlephNumbers

Think about the initial state of the springs. The tension in them can be expressed as (k1 + k2)[x][/0] and then the force F further stretches the springs to the value (k1 + k2)x. Thus, (k1 - k2)x - F = initial tension.

7. Mar 23, 2015

### stannard97

But Fafter equilibrium=ktotal*x
where Ftotal is F required to overcome initial tension+Fafter equilibrium
so Ftotal-Initial Tension=ktotal*x

8. Mar 23, 2015

### AlephNumbers

Yeah that looks good. Thank you for clearly and concisely representing the quantities.