Finding distance of a block with an unattached spring

[Robertoalva]

1. A 9 kg block is pushed by an external force against a spring with spring constant 118 N/m until the spring is compressed by 2.1 m from its uncompressed length (x= 0). The block rests on a horizontal plane that has a coefficient of kinetic friction of 0.67 but is NOT attached to the spring. After all the external forces are removed (so the compressed spring releases the mass) how far D along the plane will the block move before coming to a stop? The acceleration due to gravity is 9.8 m/s^2.

Homework Equations

U=1/2kx^2
KE= 1/2mv^2

The Attempt at a Solution

If I'm not mistaken, I have to use one of the acceleration formulas,but first i have to find the velocity of the block with the kinetic energy formula

 

[Doc Al]

I suggest using energy methods to solve this.

 

[Robertoalva]

so, i just use KE and U? and how will it be then?

 

[Doc Al]

so, i just use KE and U?

Don't forget the work done against friction.

 

[Robertoalva]

so then it will be, KE+U-W=Total Energy ?

 

[Doc Al]

so then it will be, KE+U-W=Total Energy ?

I'd put it this way. At any moment, the total mechanical energy = KE + U. The change in the total mechanical energy will equal the work done by friction.