# Statics poblem with a pre-stretched spring

I am dealing with a statics problem in the following link. This question is from the courtesy of Engineering mechanics, Statics by R.C. Hibbeler, 13th edition. Before applying vertical forces F and -F, 60 Ib of force causes 1.5 ft of stretch in springs. With the exercise of the two forces, springs stretch some more and this can be found from the geometry of the problem. This stretch is 0.27 ft at points C and D. Finally, again due to geometry F equals the force in one of the springs.

I sum the initial stretch and the final stretch and multiply this with the stiffness of one spring but do not arrive at the true answer.

What am I doing wrong here?

• What answer did you get, and what do you believe the “true answer” to be? – Jonathan R Swift Jul 27 '19 at 22:23
• You went wrong at “F equals the force in one of the springs”. F doesn’t equal the total force in the spring or the additional force above pretension. Draw a free body diagram of half of the system, not forgetting reaction forces and update your question – Jonathan R Swift Jul 27 '19 at 22:29
• As mentioned by Jonathan, please edit your question actually showing your work (not just describing it as you have), and preferably give the correct answer as given by the book, so that we can make sure our answers are correct as well. – Wasabi Jul 28 '19 at 4:08
• Draw forces at A, B, C, D due to symmetry A is same as as B and C is same as D. – joojaa Jul 28 '19 at 9:30
• @JonathanRSwift, I reconsidered the problem and realised that I made a mistake in drafting the free body diagram at point D. The correct answer is 40.8 Ib. I found it. I express my thanks to you. – Ali Kıral Jul 28 '19 at 9:36