# Bicyclist coasting down hill (Newton's Laws)

## Homework Statement

"A bicyclist can coast down a 5° hill at a constant 7.0 km/h. Assume the force of friction (air resistance) is proportional to the speed v so that Fair = cv."

(a) Calculate the value of the constant c.
(b) Calculate the average force that must be applied in order to descend the hill at 22 km/h. The mass of the cyclist plus bicycle is 79 kg.

Newton's Laws

## The Attempt at a Solution

Since a=0, Ʃforce must=0.

Fair=Fg

Fg=mgsin(5°)=Fair

c=mgsin(5°)/v

I just can't figure out how to work around not having mass in this problem.

Any help would be greatly appreciated :)

jambaugh
Gold Member
What do you mean not having mass? You say the mass of the cyclist + bike is 79kg!

PhanthomJay
Homework Helper
Gold Member
your equation is correct...the mass is given in part b. Now try part b.

I understand that the mass is given in part B. But not having the mass in the initial problem implies that mass is not needed to solve part A. I was hoping that someone could tell me how to solve part A without mass. Sorry for the confusion

PhanthomJay