# Homework Help: Block-spring Problem

1. Feb 14, 2008

### anastasiaw

1. The problem statement, all variables and given/known data
A 2- kg block rests against one end of a horizontal spring which is compressed by 18 cm. When the spring is released, the spring forces the block to slide across a table top. It stops 47 cm from where you released it. The spring constant k is equal to 120 N/m. Calculate the constant of kinetic friction μk between the block and the table.

2. Relevant equations
W=.5kx^2
W=Fd

3. The attempt at a solution
I used the two equation above to find that F=4.136N

Somebody suggested I should put this into the equation F=μk*F(n), but I don't know how to find F(n). Any help?

2. Feb 14, 2008

### Staff: Mentor

The table is horizontal. Consider the vertical forces acting on the block.

3. Feb 14, 2008

### anastasiaw

Okay, gravity? How do I apply that to this problem?

4. Feb 14, 2008

### Staff: Mentor

Gravity is one of the forces on the block.

Answer this: A block sits on the table. What normal force must the table exert on the block?

5. Feb 14, 2008

### anastasiaw

Okay I got it -- F(n) is the normal force... the weight of the object. Thanks.

6. Feb 14, 2008

### Staff: Mentor

That's it.

7. Feb 14, 2008

### WiFO215

Consider the work done by frictional force. It will be equal to?
μk x Normal Force = ?

8. Feb 14, 2008

### Staff: Mentor

That's the friction force. How do you find work?