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Car on Icy Hill

  • Thread starter bpw91284
  • Start date
67
0
1. Homework Statement
On an icy day, you worry about parking your car in your driveway, which has an incline of 13°. Your neighbor Ralph’s
driveway has an incline of 8°, and Bonnie’s driveway across the street has one of 5°. The coefficient of static friction
between tire rubber and ice is 0.15. Which driveway(s) will be safe to park in?

2. Homework Equations
Force of friction=F*u

3. The Attempt at a Solution
How can we know 'F' without knowning the mass of car?
 

Answers and Replies

cristo
Staff Emeritus
Science Advisor
8,056
72
Just let mass=m, and leave it in the equations. When comparing the components of the forces in the horizontal direction, the masses will cancel.
 
67
0
Here is what I just did...

Sum of Forces in horz direction,
F_f*cos@-F_n*cos(90-@)=0
Since F_f=u*F_n
0=0.15*F_n*cos@-F_n*cos(90-@)
Divide by F_n, solve for @ to be 8.6 degrees. So both Ralph's and Bonnie's driveways will be ok?
 

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