A car takes a flat bend of radius 110 m.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A car takes a flat bend of radius . The coefficient of static friction between the tyres and the road is when dry and when wet. Taking , what is the fastest safe speed on each road, in km/h?
Need a reminder? The key ideaShow
On a flat bend, friction supplies the force toward the centre, so . On a bend banked at , the tilted normal reaction supplies it, and no friction is needed when
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. , , .
Plan. , then change to km/h.
Step 1. Dry. , or .
Step 2. Wet. , or .
Answer: About when dry and when wet.
Check. The friction fell to about of its dry value, and the speed to about of it: . Good.
Watch out. Halving the friction does not halve the safe speed. It divides it by , because goes as .
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