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Review and Practice calculations involving Conversions, Kinematics, Newton's Second Law, Energy, Non-Conservative Forces and Power.
Activity worksheet: Click Here
Today we compare a Navy Los Angeles (688) class Submarine with the Air Force Airborne Laser (a Boeing 747 airliner). Thoughts to ponder...
- Which has the more powerful propulsion system?
- Does one speed up more quickly than the other? ...why?
688 Class Submarine
- Los Angeles (688) Class Submarines were designed as Fast-Attack submarines because their main purpose was to hunt down and kill other submarines. Among other things, they needed to be able to accelerate quickly to evade enemy torpedoes.
- They were also designed to be able to keep up with fast moving Aircraft Carrier Battle Groups, so they could sprint out in front of the carrier and make sure the path was clear of enemy ships and submarines.
- mass = 7.00 million kg
- Shaft horsepower = 34850 hp or 26 MW
- Speeds up from 0 to 20.0 knots in one minute
- Aims a basketball width laser beam, able to destroy a large incoming missile.
- Weight = 875,000lbs
- 4 engines
- Each engine generates 432,300 horsepower
- Speeds up from 0 to 175mi/hr (290km/hr) in 30.0sec
Show your work for conversions and calculations used to complete the table in the Activity Worksheet. You will need to make conversion factors out of many of these helpful conversion equalities. There are others that you will need, but you should have memorized them by now, or you can look them up.
|1 knot = 1.151 miles per hour||1 m = 3.281 feet 1mi = 5280 ft|
|1 horsepower (hp) = 746 Watts||1 pound (lb) = 4.45 Newton|
- Assume that the acceleration is constant during these problems.
- Use the speeds and the time to calculate the acceleration.
- Using the acceleration and the vehicle's mass, calculate the net horizontal force exerted during this time period.
- Calculate the power of the propulsion plant (for the 747, the power for all 4 engines combined).
- Using Kinematics, calculate the distance travelled during the period of acceleration.
- Using the rated power of the vehicle's propulsion plant, calculate the amount of energy wasted...expended by the propulsion system, but not converted into kinetic energy of the vehicle.
- Using the wasted energy and the distance, calculate the average fluid friction force experienced during the period of acceleration. How does this force compare with the weight of the vehicle?
- Calculate the factor by which the airliner value compares to the 688 value, e.g. mass(plane)/mass(sub)