(a) Calculate the value of the constant c. (b) what is the average force that must be applied given the info?

Question

A bicyclist can coast down a 5° hill at a constant 5.0 km/h. Assume the force of friction (air resistance) is proportional to the speed v so that Ffr = cv.

(b)What is the average force that must be applied in order to descend the hill at 18 km/h? The mass of the cyclist plus bicycle is 76 kg.

Answer 1

Constant speed means zero net force. So what's balancing the air friction?

Answer 2

(a)
sin(5 deg)*mg = cv
c = (sin(5)*mg)/v (v = 5 km/h = 5000 m/h = 1.4 m/s)
c = 0.61m ( where m is the mass of the object)

(b)
Fg + Favg = Ffr
Favg = (0.61m * 5 meters/sec) - sin(5)mg
Favg = 167 Newtons