Circular motion- finding angle of the banking

[wxwolf]

Homework Statement

A banked circular highway curve is designed for traffic moving at 60km/h the radius of the curve is 200m traffic is moving along the highway at 40km/h on a rainy day. what is the minimum coefficient of friction between the tires and the road that will allow cars to take the turn without sliding off the road (assume the cars do not have negative lift)


Im trying to find the angle of the banking first. i used [theta=tangent^-1(v^2/rg)] where r is the radius, v is the velocity and g is gravity.

when i do the problem out though:

=tan^-1(60km/h)^2/(.2km)(9.8m/s^2)
=tan^-1(3600)/(1.96)
=tan^-1(1836.73)
=89.96

there is no way that banking is almost 90 degrees. Where am i going wrong?

once i do that, I can plug it in and solve the problem for the kinetic coefficient.

 

[Doc Al]

You're messing up with units. Use standard units for speed (m/s) and distance (m).