Asked by Emmanuel

The resistance QR to the motion of a car is partly constant and varies as the square of the speed. At 20km/hr it is 265N. And at 30km/hr it is 365N. Find the resistance at 80km/hr
Answered by oobleck
R = a + bs
to find a and b, solve
a+20b = 265
a+30b = 365

then find a+80b
Answered by R_scott
QR = a s^2 + c

265N = a 20^2 + c = 400 a + c

365N = a 30^2 + c = 900 a + c

subtracting equations (to eliminate c) ... 500 a = 100N

solve for a , then substitute back to find c

use the new equation to find QR at 80km/hr
Answered by oobleck
oops ... my bad. I missed the "square" part.
But I'm sure you caught it before R_Scott did ... right?
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