The resistance(R) to the motion of a car is partly constant and partly varies as the square of the speed, u. When the car is moving at 30kg per hour the resistance is 630N and when the car is moving at 50kg per hour the resistance is 950N

Question

I. Find an expression for R in terms of u
II. The resistance at 80kg per hour

Answer 1

R = au^2 + b
You have two data points, so just solve for a and b in
900a+b = 630
2500a+b = 950
Then find R(80)

oh -- and speed is km/hr, not kg/hr