What is the change in kinetic energy of block A as it moves up the incline?

[madcat1090]

1. Two blocks, A and B (with mass 50 kg and 100 kg, respectively), are connected by a string, as shown in the figure below. The pulley is frictionless and of negligible mass. The coefficient of kinetic friction between block A and the incline is µk = 0.21. Determine the change in the kinetic energy of block A as it moves from C to D, a distance of 25 m up the incline if the system starts from rest.

http://img26.imageshack.us/img26/5803/p564.gif




I used
a1=-a2
T-m1g*sin37=m1a1
T-m2g=m2a2 -T+m2g=m2a1
m2g-m2a1-m1g*sin37=m1a1



3.

Solved for a (1.142 m/s^2), solved for Vf (.7556 m/s) and used the equation KE=.5mv^2. I did something wrong, but I'm not sure what. Please help

 

[rl.bhat]

Hi madcat1090, welcome to PF.
In your attempt you have not taken into account the frictional force, which acts in the opposite direction of motion of A

 

[madcat1090]

So should i use T-m1g*sin37-ukn=m1a1?

 

[rl.bhat]

So should i use T-m1g*sin37-ukn=m1a1?

Yes.
What is the normal force?

 

[madcat1090]

Yes.
What is the normal force?

Ummm, should be mg*cos37 right?

 

[Jebus_Chris]

You can also solve the problem by using energy.

 

[rl.bhat]

Ummm, should be mg*cos37 right?

Right.

 

[madcat1090]

Awesome. I think I can solve it now. Thanks for the help!