500
Why does a biker have to pedal harder at a constant speed into the wind on a windy day compared to traveling on the same road at the same speed on a calm day?
On both the calm and windy days, the net force on the biker is zero because the biker is traveling at constant speed. On a calm day, the biker must pedal so that the forward-directed force applied to the bike balances the forces of friction opposing the forward motion. The friction forces primarily take the form rolling friction and fluid friction. On a windy day, the fluid friction force is much greater, so the rider must pedal harder to maintain the same constant speed.