# Physics Help PLEASE Two hard questions I don't even know where to start

*label*Physics

*timer*Asked: Oct 5th, 2015

**Question description**

**1
**A bicyclist can coast down a 4o
hill to descend the hill at 6 Km/h. The force of
friction is proportional to speed v such that Ff = CV where C is a constant.
Calculate the average force that must be applied in order to descend the hill at 20
km/h. The mass of the cyclistplus bicycle is 80 kg

**2
**A car of mass m is going around a circular turn of radius R , that is banked at an
angle θ with respect to the ground. The force that keeps the car towards the center
of the circle F= mv2
/R. The coefficient of static friction between the tires and the
road is μ . Let g be the magnitude of the gravitational acceleration. You may neglect
kinetic friction (that is, the car’s tires do not slip).
a) At what speed v0 should the car enter the banked turn if the road is very slippery
(that is μ 0 ) in order not to slide up or down the banked turn?
b) Suppose μ tan θ < 1. What is the maximum speed v
max
with which the car can
enter the banked turn so that it does not slide up the banked turn?
c) Suppose μ tan θ < 1. What is the minimum speed v
min with which the car can
enter the banked turn so that it does not slide down the banked turn?
d) Suppose the car enters the turn with a speed v such that v
max
> v > v
0 . Find an
expression for the magnitude of the friction force.