# Physics

A spring has a force constant of 100N/m and an unstretched lenght of .07 m. One end is attached to a post that is free to rotate in the center of a smooth table. The other end is attatched to a 1 kg disc moving in uniform circular motion on the table, which stretches the spring by .03m. Friction is negligible. What is the centripital force on the disc?
a).3 N
b)3 N
c)10 N
d)300 N
e)1,000 N

So for the 1st part:to find the force I did this 100/.03 but I got 333.333 I can't figure out what i am doing wrong.

There's also a second part to this: What is the work done on the disc by the spring during one full circle?
a)0 J
b)94 J
c)186 J
d)314 J
e)628 J

Would I use W =fd where f is the answer of the above question times (.1)?

What you are doing wrong is not using Hooke's law: Force= k x

On the second, you are not thinking: W=fd is force times the distance in the direction of the force. The direction is Perpendicular to the force, so work is zero.

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1. F=kx

k=100
x=.03

F=100*.03=3N

(directed towards center b/c Centrip. force always does that)

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posted by tammy

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