Question

To maintain a constant speed, the force provided by a car’s engine must equal the drag force plus the force of friction of the road (the rolling resistance). what are the drag forces at 50 km/h and 80 km/h for a toyota camry? (drag area is 0.67 m2.)

Answer 1

Given:
A = 0.67 m², the area perpendicular to the direction of motion
v = 50 km/h and 80 km/h, traveling speeds

The drag force is
F = (1/2) CρAv²
where
C = 0.4, the drag coefficient (a low number for efficiently designed Camry)
ρ = 1.225 kg/m³, density of air

Note that 1 km/h ≈ 0.2778 m/s.
Therefore,
50 km/h = 13.89 m/s
80 km/h = 22.224 m/s

At 50 km/h, the drag force is
F₅₀ = 0.5*0.4*(1.225 kg/m³)*(0.67 m²)*(13.89 m/s)² = 31.67 N
At 80 km/h, the drag force is
F₈₀ = 0.5*0.4*1.225*0.67*22.224² = 81.075 N

Answers:
31.7 N at 50 km/h
81.1 N at 80 km/h