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lala56

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**HW question, help, momentum**

"A 0.150 kg frame, when suspended from a coil spring, stretches the spring 0.05 m. A 0.2 kg lump of putty is dropped from rest onto the frame from a height of 30.0 cm (Fig. 8.38). Find the maximum distance the frame moves downward from its initial position."

This problem has been posted before, but I have been unable to use it to solve my question

so, here is what I tried:

the k for the spring = 29.4 using F=kx

then

i found the velocity of the putty as soon as it touched the frame

mgh=.5mv^2

v=2.42

now, find the velocity of the system (putty and the frame)

Mp=mass of putty

Vp=velocity of putty

Mf=mass of frame

MpVp=(Mp+Mf)V2

plug the v found above into Vp, and then V2=1.39

so, now use this:

K1+U1+Ue1=K2+U2+Ue2

K1=kinetic energy

U1= potential energy (gravity)Ue1 = potential energy (spring)

i get:

.5(.2+.15)(1.39)^2 + .5(29.4)(.05)^2 + mgh = .5(29.4)x^2 + mgx

this is how I believe it should be done, except I don't know what to put in place of the "mgh". What is the original potential energy before the spring stretches.

I basically need to find the "x".

thanks, any help is greatly appreciated

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