Acceleration of block down an incline

[aliaze1]

Homework Statement

Find the acceleration of block A when moving downward

Theta=40 degrees
A=103N
B=31N
Static coefficient = 0.56
Kinetic coefficient = 0.25

Homework Equations

F=ma
Normal Force * Kinetic coefficient = Friction Force

The Attempt at a Solution

From 103/9.8 I get a mass of ~10.5

Breaking 103 into components, 103sin40 and 103cos40, the first being perpendicular and the second being along the plane

103sin40*0.25=Friction Force

Tension is 31, so the sum of forces is:

(31+103sin40*0.25)-103cos40 = Fnet

Fnet/10.5 = Acceleration of A

is this correct?

Thanks!

 

[jumpman11372]

you have mixed up the normal force and the force going down the ramp

mgcos40 would be the FN ; use this to find the frictional force
mgsin40 would be the force with which it accelerates down the ramp

try writing some net force equations ; those would help :]