Find an expression for the COF

[Mille89]

Homework Statement

Hi! I am working on a lab-report where we have measured the time a body use up a inclined plane.
i am going to find a expression for the coefficient of friction expressed by the time and acceleration that i have found.

This expression do i need for the next task where i am going to find the kinetic friction.

But i have no idea how i can find the expression

Homework Equations

= f/N

The Attempt at a Solution

= 1/2*at²

 

[haruspex]

going to find a expression for the coefficient of friction expressed by the time and acceleration that i have found.

Please describe the experiment in more detail, in particular what measurements were taken.
What forces acted on the body? Which of them had components in the direction of the acceleration?
What equation (ΣF=ma) can you write?

 

[Mille89]

This lab exercise was about Newtons 2 law.
Where we where going to find:

• The angle of the plane (30)
• Find the lengst of the plane (0.93m)
• Measure the time up the plane with different underlay, 5 times each.
• The constant acceleration and compare it with the sum of the forces on the box
• And Then find the expression for the COF...

I have measured the time a plasticbox(0.0959 kg) use up the plane (length 0.93m). I did this 5 times and found out that the mean was 1.335 s.

Then i used s=vt+1/2*at²
0.93m=0*1.335s+1/2a(1.335s)²
a=2*0.93m/(1.335s)²
a=1.04m/s²
Hmm I think this is wrong i see now that its the constant acceleration i am going to find.

Its like 10 years since i had physics last, so i have forgoten a lot of it and we where two on this task but right now its only me working on it

m1(plasticbox) =0.0959kg
m2(Weight, power source) = 0.2kg

 

[haruspex]

I think this is wrong

No, your estimate of the acceleration looks fine.
What you need now is the force versus acceleration equations for the two masses.
Draw a separate Free Body Diagram for each.
Write out the ΣF=ma equation for the suspended mass.
For the mass on the ramp, what components of forces act along the slope?

 

[Mille89]

The acceleration for the two masse is the same a_m1m2=2*s/t² = 2*0.93m/(1.335s)²= 1.04m/s²

The force:
ΣF=ma
G_x= mgsin(30) = 0.470N
Is ΣF Then 0.470N on the mass 1?

 

[haruspex]

Gx= mgsin(30) = 0.470N
Is ΣF Then 0.470N on the mass 1?

No, that's just Gx. There are two other forces parallel to the ramp.