Given:
The required frictional force to turn on a road is,

while the bicycle is moving at a speed of

To find:
The frictional force required to make the same turn at a speed of 2v
Step-by-step explanation:
The required frictional force should be equal to the centrifugal force. So, we can write,

Now, for the speed 2v, the frictional force is,

Hence, the required force is 4F.