Harry Hotrod rounds a corner in his sports car at 50 km/h. The friction force holds him on the road. If he has twice the speed, what must be the friction force to prevent him from skidding off the road?

The friction must counteract (and equal) the outward acceleration defined by:

eq 1) a = v

^{2}/rAnd the friction force can be found with

F= ma, subsituting eq 1) F=mv

^{2}/rFor this problem mass and radius are constants.

Let F1 equal the friction force at 50 km/h.

Let F2 equal the friction force at 100 km/h (2x50)

If we set this up as a ratio:

F1 mv

^{2}/r---- = -------

F2 m(2v)

^{2}/rthe m, r and v

^{2}cancel from the equation and we are left with 1/4.The friction force at 100 km/h must be 4 times larger than it was at 50 km/h.

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