Question

Rent a rideshare bike and ride it throughout the course at a pace that elevates your heartbeat
somewhat, but without over-exertion. Time your ride and calculate your average speed. Draw a
force diagram for the bicycle’s motion, and label it with estimates of each force. Calculate the
power you used during your ride to maintain your average speed, in watts and then in
horsepower. Calculate the (exercise) Calories you burned during your ride. (My time was 8.23 minutes for 1.3 miles)

Rent a rideshare scooter and ride it throughout the same course at a safe speed. Try to go
somewhat faster than the bike, but most importantly stay safe. Time your ride and calculate your
average speed. Draw a force diagram and label it with estimates of each force. Calculate the
power used by the electric motor to maintain your average speed, in watts and then in
horsepower. (My time was 1.2 miles for 11minutes and 10mph.)
In both calculations, include estimates for resistance from both surface friction and air. You will
need to research a plausible (e.g., order of magnitude) estimate for (a) the coefficient of rolling
friction from the wheels (used in the same way as the coefficient of kinetic friction we discuss in
class problems), and (b) drag from air resistance. Which is larger?

MAke sure to calculate air resistance and friction resistance for the bike and scooter. Draw force diagrams for the bike and scooter.

Answer 1

Bike

v = dist/time = 1.3 miles/ 8.23 min = 4.21 m/s

Assuming W = 1000N = R... for biker and biker

Taking n = 0.002 between tyre and road
nR = 20N

Fd = r cw A vwind2 /2	where	r :	density of air in kg/m3 = 1.2 kg/m^3
		cw :	coefficient of wind resistance, dimensionless = 1 assumed
		A :	frontal area in m2 = 0.5 m^2 approx
		vwind :	wind velocity in m/s = 5 m/s assumed relative to bike

Fd = 7.5N

F = Fd + nR = 27.5N

P = Fv = 27.5 x 4.21 = 115.78W = 0.155 HP
*1 HP = 746 W

kCalories burnt = 115.78 x 8.23 x 60 / 4200 = 13.6 kCal

*1kCal = 4200 J and energy = power x time

B) SCOOTER

v = dist/time = 1.2 miles/ 11 min = 2.91 m/s

Assuming W = 2500N = R... for rider and scooter

Taking n = 0.002 between tyre and road
nR = 50N

Fd = r cw A vwind2 /2	where	r :	density of air in kg/m3 = 1.2 kg/m^3
		cw :	coefficient of wind resistance, dimensionless = 1 assumed
		A :	frontal area in m2 = 0.8 m^2 approx
		vwind :	wind velocity in m/s = 3 m/s assumed relative to bike

Fd = 4.32N

F = Fd + nR = 54.32 N

P = Fv = 54.32 x 2.91 = 158W = 0.21 HP