# Homework Help: Finding distance of a block with an unattached spring

1. Jul 5, 2013

### 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.

2. Relevant equations
U=1/2kx^2
KE= 1/2mv^2

3. 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

2. Jul 5, 2013

### Staff: Mentor

I suggest using energy methods to solve this.

3. Jul 5, 2013

### Robertoalva

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

4. Jul 5, 2013

### Staff: Mentor

Don't forget the work done against friction.

5. Jul 5, 2013

### Robertoalva

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

6. Jul 5, 2013

### Staff: Mentor

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.