Final answer:
To maintain a constant velocity on a bike, the force of friction is equal and opposite to the force applied by the rider. Therefore, if a rider applies a force of 85 N, the frictional force is also 85 N acting in the opposite direction.
Step-by-step explanation:
If you are riding a bike at a constant velocity and applying a force of 85 N, the force of friction acting on the bike can be determined using Newton's first law of motion. According to this law, if there is no acceleration, then the forces are balanced, meaning that the net force is zero. Since you're riding at a constant velocity, all forces must be balanced, including the force you apply and the force of friction.
Therefore, if the only two forces acting along the direction of motion are your 85 N force and friction, the force of friction must be equal and opposite to the force you apply to maintain a constant velocity. Hence, the force of friction acting on the bike is 85 N, but in the opposite direction to your applied force.
It's important to note that this is a simplified scenario assuming a flat surface and ignoring other potential forces such as air resistance. Additionally, if there are any other forces acting horizontally, such as air resistance, they would need to be accounted for to determine the actual force of friction..