If 7.00hp are required to drive a 1500-kg automobile at 66.0 km/h on a level road. What power is necessary to drive the car at 66.0 km/h down a 1.00 % grade? It requires 42.9 hp to drive the car at 66.0 km/h up a 10.0 % grade (a hill rising 10.0 m vertically in 100.0 m horizontally)? The total retarding force due to friction, air resistance, and so on is 285 N.

Question

If 7.00hp  are required to drive a 1500-kg automobile at 66.0 km/h  on a level road. What power is necessary to drive the car at 66.0 km/h down a 1.00 %  grade? It requires 42.9 hp to drive the car at 66.0 km/h up a 10.0 % grade (a hill rising 10.0 m vertically in 100.0 m horizontally)? The total retarding force due to friction, air resistance, and so on is 285 N.

drwls · Answer

Is the following a statement of fact or a question? << It requires 42.9 hp to drive the car at 66.0 km/h up a 10.0 % grade (a hill rising 10.0 m vertically in 100.0 m horizontally)? >>

Allison · Answer

It is a fact.

drwls · Answer

Then why the question mark at the end?

Assume 35.9 extra hp is needed to provide the potential energy increase at that speed and 10% positive slope. At 1/10 the slope (1%) downwards, 3.6 hp is recovered from gravity, so the engine needs to provide only 3.4 hp.