heres the problem

http://i14.photobucket.com/albums/a3...ristx/adsf.jpg

heres my work

http://i14.photobucket.com/albums/a3...istx/faaaa.jpg

The speed is supposed to be 5.18 but im not getting that...

any ideas?

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- May 9th 2008, 10:26 AMjason03Work/energy
heres the problem

http://i14.photobucket.com/albums/a3...ristx/adsf.jpg

heres my work

http://i14.photobucket.com/albums/a3...istx/faaaa.jpg

The speed is supposed to be 5.18 but im not getting that...

any ideas? - May 9th 2008, 12:18 PMDanshader
ok first i am going to convert all the units given in tat question to SI units (i was taught in SI units)

mass of the collar, m = 0.17 kg (1 oz = 0.0283495231 kg)

spring constant, k =875.83 N/m (1 lb/in = 175.166 N/m)

distance spring compressed, x = 0.0381 m (1 inch = 0.0254 m)

Now total elastic potential energy,EPE stored in the spring before release is given by the formula,

The collar is then released. At point B, the collar has already traveled 10 inches (0.254 m) vertically upwards.

Hence gravitational potential energy,GPE gained by the collar is:

using principle of conservation of energy the total energy of the system is conserved:

Initial energy = final energy

EPE = Kinetic energy + GPE

0.635681793J = KE + 0.4235958J

KE = 0.21085993 J

from the formula of kinetic energy, KE:

well as for the force part take note that:

elastic potential energy, EPE = - May 9th 2008, 02:13 PMjason03
Thanks!....that really helped.....i realized one of my big problems was converting the spring constant which is what I forgot......I like working in metric better as well.....U.S. Customary is a pain.....

What is the strategy for finding the force the collar is putting on the rod? - May 9th 2008, 09:47 PMDanshader
the motion of the collar now is in a circle, hence we can consider centrifugal and centripetal force acting on the collar.

well you have already calculated the linear speed,v (do not confuse with angular speed ) of the collar previously also r and m are given in the question. Hence just substitute those values into equation (1) and solve for F remember to state the direction of the force on the collar as well which in this case at point B is inwards (towards the left/ towarsd the center of the circle) - May 10th 2008, 02:39 AMtopsquark
Two comments:

Be VERY careful here. . If you aren't careful your spring potential energy will be the negative of what you are looking for!

Never consider the centrifugal force unless you are working with a relative motion problem.

-Dan