(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A spring is stretched a distance of Dx = 40 cm beyond its relaxed length. Attached to the end of the spring is an block of mass m = 11 kg, which rests on a horizontal frictionless surface. A force of magnitude 35 N is required to hold the block at this position. The force is then removed.

a) When the spring again returns to its unstretched length, what is the speed of the attached object?

b) When the spring has returned only halfway (20 cm), what is the speed of the attached object?

2. Relevant equations

W = 1/2*m*v^2

3. The attempt at a solution

I have already solved part a. First I calculated the spring constant by 35 = k*0.4 which means k = 87.5

Then I did .5*k*x^2 = .5*m*v^2 and solved for v which is 1.128m/s

For part b I assumed I would just change the x in the above equation to 0.2 instead of 0.4 which would be 0.564 but it is wrong. So I thought the spring constant would change as well so I tried it again changing the k also but it is also not right. What am I doing wrong?

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# Homework Help: Block on Spring without Friction and speed

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