Friction Forces and max braking force

[DeadFishFactory]

1. The coefficient of static friction between the tires of a car and a dry road is .62. The mass of the car is 1500 kg. What is the maximum braking force is obtainable:
a. horizontal to the road.
b. on an 8.6 degree downgrade?



2. F=mA f(s)=M(s)N N=mg F=f(s)-mgsin(x)



3.
a. f(s)=.62(9.8)(1500)sin90=9114 N
b. f(s)=.62(9.8)(1500)sin8.6=2198 N

My problem is that "b" isn't correct, I checked the back of the book I was using and they got 9000 N. Can anyone show me how to do this problem? I know I suck at physics. Also, if possible, can anyone explain to me how to find the tension of a string? Thanks!

 

[Dick]

If horizontal is 90 degrees, then 8.6 degrees downgrade must be 81.4 degrees. Most people would probably call horizontal 0 degrees and use a cos instead of sin. The tension on a string is "how much it pulls", sorry but that question is really vague.