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odie5533
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Homework Statement
(A) If 18.5 HP are required to drive a 2320 kg automobile at 62.0 km/h on a level road, what is the total retarding force due to friction, air resistance, and so on?
(B) What power is necessary to drive the car at 62.0 km/h up a 15% grade (a hill rising 15.0m vertically in 100m horizontally).
The Attempt at a Solution
18.5 HP = 13795 W
62.0 km/h = 17 m/s
A) [tex]P = F*v[/tex]
[tex]P / v = F[/tex]
[tex]F = ma[/tex]
[tex]P / v = ma[/tex]
[tex]a = P / (v * m)[/tex]
[tex]13795 / (17 * 2320) = 0.3498N[/tex]
B) [tex]\alpha = arctan(15/100) = 8.53[/tex]
[tex]\sum F = F_{up} - 0.3498N - w sin(8.530)[/tex]
[tex]\sum F = F_{up} - 0.3498N - 3375N[/tex]
[tex]F_{up} = 3375N[/tex]
[tex]P = F * v[/tex]
[tex]P = 3375 * 17 = 57375 W = 77 HP[/tex]
This seems completely wrong to me... I'm not sure if any of it is right even. Any help would be greatly appreciated.