Acceleration of block down an incline

AI Thread Summary
The discussion focuses on calculating the acceleration of block A moving down an incline at a 40-degree angle, given its weight and friction coefficients. The user initially calculates the mass of the block and attempts to break down the forces acting on it, including friction and tension. However, a correction is suggested regarding the normal force, indicating that the user confused it with the force acting down the ramp. The correct approach involves using mgcos40 for the normal force and mgsin40 for the force accelerating the block down the ramp. The conversation emphasizes the importance of accurately applying net force equations to solve for acceleration.
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Homework Statement


06_38.gif


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!
 
Last edited:
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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 :]
 

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