Calculating Kinetic Energy in English Units

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To calculate the change in kinetic energy of an object with a mass of 10 lbm as its velocity decreases from 50 mph to 15 mph, it is essential to convert the mass into slugs for accurate results. The formula for kinetic energy is KE = 1/2 mv^2, where velocity must be converted from mph to ft/s using the conversion factor of 1 mph = 1.4667 ft/s. The mass in slugs can be determined by dividing the weight in pounds by the acceleration due to gravity (32.17 ft/s²). This approach ensures that the final kinetic energy is expressed in foot-pounds force (ft·lbf). Understanding these unit conversions is crucial for solving problems in English units effectively.
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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.
 
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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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