Equilibrium. On your way to Ankara from $$stanbul$,$ there are two inclines, one uphill and one downhill, both with a $15\%$ grade. Your hatchback, which has a mass $900kg,$ achieves a steady speed of $100k\frac{m}{h}$ when freewheeling downhill, and can ascend the incline at a steady speed of $90k\frac{m}{h}$ under power $($if you go full throttle$)$ and under the same road and wind conditions. What is the effective horsepower of your car? Indicate the assumptions in your estimation ${?}^5.$