Force on an Incline Plane Problem HELP

[whoopie88]

Homework Statement

A 63-kg person on skis is going down a hill sloped at 30° from the horizontal. The coefficient of friction between the skis and the snow is 0.20. What would be the magnitude of the acceleration?

Homework Equations

f=ma
fg=mg
fnet=mAnet
Ff=μῦFn

The Attempt at a Solution

I got -102.14, but I'm supposed to put it in as 102.14 right? Because the magnitude is the absolute value of whatever I get..? I found Fnet by subtracting Ff from Fg,x. I got 535.23 for Fn.

PLEASE HELP!? I put in 102.14 on the Webassign but it came back as wrong.

Thank you all!

 

[rl.bhat]

Show your calculations.

 

[whoopie88]

Fn = Fg,y
Fn = mgcos30
Fn = 63(9.81)cos30
Fn = 535.23

Fnet = mgsin30 - μῦFn
mAnet = mgsin30 - μῦFn
Anet = gsin30 - μῦFn
Anet = 9.81sin30 - 0.2(535.23)
Anet = -102.14

And as I mentioned earlier, I changed it to positive 102.14.

Thanks for your time.

 

[rl.bhat]

mAnet = mgsin30 - μῦFn

The above equation should be

m*Anet = m*g*sin(30) - μ*m*g*cos(30)

Now solve for A.

 

[whoopie88]

Thank you for your help, I didn't realize m canceled out for the Fn formula until you showed me how I could use substitution. Thank you!