Find acc. given coefficient of frict. on incline slope

[shizupple]

1. The problem statement, all

variables and given/known data
A clerk moves a box of cans down an

aisle by pulling on a strap attached to

the box. The clerk pulls with a force

of 190.0 N at an angle of 28° with the

horizontal. The box has a mass of 37

kg, and the coefficient of kinetic

friction between the box and the floor

is 0.45. Find the acceleration of the

box.

Homework Equations

Ff=U*Fn

The Attempt at a Solution

I tried solving this three times. I

found x and y components:
X:167.8N
Y:89.2N

Tried to find the Fn:
cos(28)89.2= 78.8N

Ff=.45(78.8)
Ff=35.5N
Fa=190-35.5N= 154.6N

154.6N=37a
a=4.2N

I also tried subtracting the force

parallel by the force applied and got

the wrong acceleration also. Am I

finding the Force Normal wrong? Some

direction would be great thanks.

 

[shizupple]

anyone know what I'm doing wrong here?

 

[hage567]

found x and y components:
X:167.8N
Y:89.2N

OK, this is fine.

Tried to find the Fn:
cos(28)89.2= 78.8N

This is not correct. Are you trying to find your normal force based on the applied force?

You have forgotten to include the weight of the box anywhere in your calculation.

The normal force will be the difference between the weight of the box and the component of the applied force in the vertical direction. When doing problems like this, you must consider all forces in each direction. Make sure to start by drawing a diagram with all of the forces showing. Then sum them up in each direction, to get your equations.