Energy Conservation & Potential Energy Spring/Friction Problem

[Help1212]

Homework Statement

A 0.80-kg block is held in place against the spring by a 67-N horizontal external force. The external force is removed, and the block is projected with a velocity v1 = 1.2 m/s upon separation from the spring. The block descends a ramp and has a velocity v2 = 1.9 m/s at the bottom. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction is 0.39. The velocity of the block is v3 = 1.4 m/s at C. The block moves on to D, where it stops. In Fig. 7.4, the force constant of the spring is..

Homework Equations

K1 +U1 +W other = K2+ U2.. ect .. U2=0.5kx^2 .. K1=(0.5)mv^2

The Attempt at a Solution

I've tries solving the problem with the equation above but I really just don't know where to start especially since there are no units of distance given.. Can someone lead me in the right direction please?

 

[tiny-tim]

Hi Help1212!

(try using the X² and X₂ icons just above the Reply box )

I assume you can find kx and kx²/2 ?

ok, then k = … ?

 

[Help1212]

euhh... I'm still a little confused..how do i find k if I don't know x?

 

[tiny-tim]

x is twice kx²/2 divided by kx

 

[Help1212]

hmm. well when I move around the equation i get k=2[0.5(mv²₂)/x²

from the assumption that K₁ + U₁ = K₂ + U₂

Am i going in the right direction??

 

[tiny-tim]

can you find kx and kx²/2 ?

if so, what are they?