Hence, the radius of CM's path is
So the total friction force must equal to
Hence, the x and y component of the friction is
Now, draw the friction forces work on both wheels. Each friction has perpendicular direction to each wheel. Sum of these two frictions must equal to the total friction (both in x and y direction).
First, for y-direction,
From equation (5), we can get
Then for x-direction,
Substitute fx from equation (4) and f2 from equation (6),
From equation (6) and (7) above, we can see that f2 is greater than f1, so the coefficient of friction must equal to
For the normal forces, because the CM of the scooter is at the middle, we can say that
And the total normal forces must equal to its weight, so
Back to coefficient of friction. From equation (6) and (8), we can get the coefficient of friction,
That's my solution.
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