Homework Help: Physics - work done by a spring

1. Feb 18, 2005

Felix83

A moving 4.90 kg block collides with a horizontal spring whose spring constant is 437 N/m.

The block compresses the spring a maximum distance of 6.50 cm from its rest position. The coefficient of kinetic friction between the block and the horizontal surface is 0.190. What is the work done by the spring in bringing the block to rest?

The Part after that is to find the work done by friction, which I got correct. The last part is to find the initial velocity of the block, I could just add the work done by friction and the spring and then solve for v with the KE formula.

However, I cant seem to find the work done by the spring to bring the block to rest. Wouldn't you just use the formula W=(1/2)kx^2 ? I used that and got 0.923 J, which the program says is incorrect.

2. Feb 18, 2005

dextercioby

Obviously there has to be a minus in the result,so it should be -0.923J.Indeed,to me,that seems to be the answer,the dork done by the elastic force acting on the body is - the elastic potential energy...
Weird,maybe something is evading my senses,but,for now,i'd say that's the correct result.

Daniel.

3. Feb 18, 2005

xanthym

Appears that {Work Done By Spring}=(-0.923 J), {Work Done by Friction}=(-0.594 J), and {Initial Velocity}=(+0.787 m/sec) should be correct.

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4. Feb 18, 2005

Felix83

yea those are the numbers i got too, but i put the friction in as positive and it said correct so i figured since the spring was pushing in the same direction it would be positive too. but these problems are dumb sometimes so i tried negative 0.923 and of course that was right. :grumpy: