# Banked Curves Section 5.4.

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Banked Curves Section 5.4

5.4 Banked Curves When a car travels around an unbanked curve, static friction provides the centripetal force. By banking a curve, this reliance on friction can be eliminated for a given speed.

Derivation of Banked Curves
A car travels around a friction free banked curve Normal Force is perpendicular to road x component (towards center of circle) gives centripetal force y component (up) cancels the weight of the car Insert Figure 5.11

Derivation of Banked Curves
Divide the x by the y Gives Notice mass is not involved Ask what happens when go to fast? (slide up and over top of curve) Ask what happens when go to slow? (slide down curve)

Example You are in charge of designing a highway cloverleaf exit ramp. What angle should you build it for speed of 35 mph and r = 100m? 13.9 35 mph = 15.6 m/s Tan  = v2/rg  tan  = (15.6 m/s)2/((100m)(9.8 m/s2))  tan  =   = 13.9

Conceptual Problem In the Daytona International Speedway, the corner is banked at 31 and r = 316 m. What is the speed that this corner was designed for? v = 43 m/s = 96 mph Cars go 195 mph around the curve. How? Friction provides the rest of the centripetal force tan  = v2/rg  tan 31 = v2/(316m)(9.8m/s2)  .6009(316m)(9.8m/s2) = v2  1861 (m/s)2 = v2  v = 43 m/s

Practice Problems See if you can speed your way around these!
Total of 4 problems

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