1. Horsepower is expressed in units of ______________ . a. Pound-feet b. Foot-pounds c. Foot-pounds per minute d. Pound-feet per second
2. A normally aspirated automobile engine loses about ______________ power per 1,000 ft of altitude. a. 1% b. 3% c. 5% d. 6%
3. One cylinder of an automotive four-stroke cycle engine completes a cycle every ______________ . a. 90 degrees b. 180 degrees c. 360 degrees d. 720 degrees
The correct answer and explanation is:
Correct Answers:
- c. Foot-pounds per minute
- b. 3%
- d. 720 degrees
Explanation:
1. Horsepower is expressed in foot-pounds per minute
Horsepower (HP) is a unit of power that quantifies the rate at which work is done. The standard definition, established by James Watt, states that one horsepower equals 33,000 foot-pounds per minute. This means an engine producing one horsepower can lift 33,000 pounds one foot in one minute. Since power is the rate of doing work, and work is measured in foot-pounds (force × distance), the correct unit is foot-pounds per minute.
2. A normally aspirated automobile engine loses about 3% power per 1,000 ft of altitude
A naturally aspirated engine relies on atmospheric pressure to draw in air for combustion. As altitude increases, air pressure and oxygen density decrease, reducing the amount of oxygen available for combustion. Since power output depends on air and fuel intake, a 3% reduction per 1,000 feet is a general rule of thumb. This means at 5,000 feet, the engine loses about 15% power. Turbocharged and supercharged engines are less affected because they force more air into the engine, compensating for lower air density.
3. One cylinder of a four-stroke engine completes a cycle every 720 degrees
A four-stroke engine operates in four stages: intake, compression, power, and exhaust. Each stage requires 180 degrees of crankshaft rotation, completing the full cycle in 720 degrees (180 × 4). Since the crankshaft rotates twice for each power stroke, this means one power stroke occurs every 720 degrees of crankshaft rotation.
Image Generation:
I’ll now generate an image illustrating the four-stroke engine cycle, showing the movement of the piston through the 720-degree cycle.
Here is a technical diagram illustrating the four-stroke engine cycle, showing the Intake, Compression, Power, and Exhaust strokes along with piston movement and crankshaft rotation of 720 degrees. Let me know if you need any modifications or further explanations! 🚗💨
