When an automobile moves with constant speed down a highway, most of the power developed by the engine is used to compensate for the mechanical energy loss due to frictional forces exerted on the car by the air and the road. If the power developed by the engine is 195 hp, estimate the total friction force acting on the car when it is moving at a speed of 30 m/s. One horsepower equals 746 W.

When its 75 kW (100 hp) engine is generating full power, a small single-engine airplane with mass 700 kg gains altitude at a rate of 2.5 m/s 1150 m/min, or 500 ft/min2. What fraction of the engine power is being used to make the airplane climb? (The remainder is used to overcome the effects of air resistance and of inefficiencies in the propeller and engine.)

A sledge loaded with bricks has a total mass of 18.9 kg and is pulled at constant speed by a rope inclined at 19.5° above the horizontal. The sledge moves a distance of 19.8 m on a horizontal surface. The coefficient of kinetic friction between the sledge and surface is 0.500. (a) What is the tension in the rope? ____N(b) How much work is done by the rope on the sledge? _______kJ(c) What is the mechanical energy lost due to friction? _____kJ

A manufacturer uses an elevator to move items from one level to another. The elevator has a mass of 700 kg and moves upward with constant acceleration for 3.00 s until it reaches its cruising speed of 1.75 m/s. (Note: 1 hp = 746 W.) (a)What is the average power (in hp) of the elevator motor during this time interval? (b)What is the motor power (in hp) when the elevator moves at its cruising speed? (c)What If? If the elevator motor can only deliver constant power at one setting, the amount needed for its motion at constant speed, how long (in s) will it take the elevator to accelerate to the cruising speed of 1.75 m/s? (If you need to use or –, enter INFINITY or –INFINITY, respectively.)