# Find the coefficent of friction of one block

1. Jul 7, 2013

### Robertoalva

1. Two blocks are connected by a light string that passes over a frictionless pulley as in the figure. The block of mass 8.24 kg lies on a horizontal surface and is connected to a spring of force constant 335 N/m. The system is released from rest when the spring is unstretched.
If the hanging 14.7 kg block falls a distance 0.653 m before coming to rest, calculate the coefficient of kinetic friction between the block m1 and the surface. The acceleration of gravity is 9.8 m/s^2

2. Relevant equations

m2gh=m1gμ - 1/2 kx^2

3. The attempt at a solution

as the equation says, i just try to solve for the coefficient of friction by substituting the values. am I wrong?

2. Jul 7, 2013

### lewando

The units of your stated equation are not consistent. Therefore, that equation is wrong. How did you come up with that equation?

3. Jul 7, 2013

### Robertoalva

well, m1gmew is because the gravity acts down on it, mew is against it so everything acts on that fragment of the system, then the m2gh is the same but now with the height actin too, and then the hook's law is just subtracting from the system

4. Jul 7, 2013

### lewando

Your equation is messed up because you have: [energy] = [force] - [energy]. If you are going to do this problem using an energy balance, what is the energy gained or lost from the 3 components?

5. Jul 7, 2013

### Robertoalva

energy+energy= force?

6. Jul 7, 2013

### lewando

Seriously, no.

1. What is the energy gained (or lost--please specify so I know you are paying attention ) by the spring?
2. What is the energy gained (or lost--please specify--same reason) by m2?
3. How much engery is required to move m1 over the stated distance?

How would they balance?

7. Jul 7, 2013

### Robertoalva

well, wouldn't it be, energyrequired to move m1= energyspring-energym2 ?

8. Jul 7, 2013

### lewando

Consider this: Ʃ(energy sources) = Ʃ(energy sinks).

What are the energy sources? Sinks?