v=70km/hr (convert to m/s) 70km/hr(1000m/1km)*(1hr/3600s)=19.4m/s
First draw a free body diagram what are your forces?
Fg pulls straight down
Fn is perpendicular to the surface
Ffs is going to point along the surface "down" the angle (or towards the center of the circle
If we define x as along the surface and y as perpendicular to it:
Fn has no x-component and Ffs has no y-component so we only have to break gravity up.
Draw a triangle and you should get:
Now that we make Fnet equations:
Fnety=Fn-Fgy Since there is no acceleration in the y plug in zero Fn=Fgy
The x is a little trickier, are Fgx and Ffs pointing in the same or opposite directions? They both point "down" the incline, or towards the center of the circle.
Now the net force in the x provides our acceleration, since our acceleration is centripetal not tangential the net force is the centripetal force.
Then substitute in
Solve for μs
plug in values