An experimental solar car developed by 70 students taking fluid mechanics course
ID: 2995972 • Letter: A
Question
An experimental solar car developed by 70 students taking fluid mechanics course at the University of North Dakota has the following characteristics: The resistant to motion consists of rolling resistance and aerodynamic drag. The rolling resistance is the product of the coefficient of rolling friction and the weight of the moving object. The average air temperature during a typical racing period is 10 degree. Determine the minimum power that has to be supplied by a lithium-ion battery to move the car forward at 75 mph (33.5 m / s) on a level race track. Determine the extra power required when there is a head wind of 15 mph (6.7m / s) and the same car speed is to be maintained.Explanation / Answer
Density of air(p) at 10 C and 1 atm = 1.2438 kg/m^3
Drag Force (Fd) = 0.5*Cd*p*V^2*A
p = density of air
Cd = coefficient of drag
V = relative velocity of vehicle with air
A = Frontal Area
Friction force(f) = umg
u = coefficient of rolling friction
m = mass of body
a) Fd = 0.5*0.2*1.2438*33.5^2*0.9 = 125.627 N
f = 0.05*850*9.81 = 416.925 N
Total Force = Fd + f = 542.552 N
since both drag and f is in opposite directio to velocity
Power = |F.V| = 542.552*33.5 = 18175.492 W
(b) with head wind = 6.7 m/s
relative velocity = 33.5+6.7 = 40.2 m/s
f will remain same
Fd = 0.5*0.2*1.2438*40.2^2*0.9 = 180.903 N
total force , F = Fd + f = 597.828 N
New Powe required = Fd*V = 24032.6956 W
extra power required = 24032.696 - 18175.492 = 5857.194 W
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