Calculating Kinetic Energy in English Units

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SUMMARY

The discussion focuses on calculating the change in kinetic energy for an object with a mass of 10 lbm as its velocity decreases from 50 mph to 15 mph. The kinetic energy formula used is KE = 1/2 mv², where mass must be converted to slugs for accurate calculations in English units. Specifically, the mass in slugs is derived by dividing the weight in pounds (10 lbf) by the acceleration due to gravity (32.17 ft/s²). This approach ensures that the resulting kinetic energy is expressed in foot-pounds force (ft·lbf).

PREREQUISITES
  • Understanding of kinetic energy formula KE = 1/2 mv²
  • Knowledge of unit conversion between lbm, lbf, and slugs
  • Familiarity with English units of measurement
  • Basic principles of physics related to mass and weight
NEXT STEPS
  • Learn about unit conversions between lbm, lbf, and slugs in detail
  • Explore the implications of using different units in physics calculations
  • Study the effects of velocity changes on kinetic energy
  • Investigate other applications of kinetic energy calculations in engineering
USEFUL FOR

Students in physics or engineering courses, educators teaching mechanics, and professionals involved in mechanical design or analysis who require a solid understanding of kinetic energy calculations in English units.

Chemmajor2017
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Homework Statement


An object has a mass of 10 lbm.

b. Find the change in kinetic energy ft·lbf when its velocity decreases from 50 mph
to 15 mph.

Homework Equations


KE=1/2mv^2
Ke=(ft*lbf)
1MPH=1.4667 ft/s

The Attempt at a Solution


When calculating this, does it need to be in slugs, lbm, or lbf?
I'm not too familiar with english units.
 
Physics news on Phys.org
the lbm unit is seldom used anymore, but an object that weighs 10 pounds (10lbf) on Earth has a mass of 10 lbm. But when using the formulas for the value of m, you must use the mass unit of slugs. The value of the slug can be found by dividing the objects weight (in pounds) on Earth by 32.17 (the acceleration of gravity). This will give the correct units (ft and lbf) for the values you are seeking, without using a conversion factor in your equations.
 

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