Calculating Kinetic Energy in English Units

In summary, when calculating the change in kinetic energy for an object with a mass of 10 lbm and a velocity decreasing from 50 mph to 15 mph, the units used should be in slugs rather than lbm or lbf. The value of the slug can be found by dividing the object's weight (in pounds) on Earth by 32.17, and this will give the correct units (ft and lbf) for the calculation of kinetic energy without requiring a conversion factor.
  • #1
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.
 
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  • #2
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.
 

1. What is kinetic energy and how is it calculated in English units?

Kinetic energy is the energy an object possesses due to its motion. It is calculated using the formula KE = (1/2)mv^2, where m is the mass of the object in pounds and v is the velocity in feet per second.

2. How is the mass of an object determined in English units?

The mass of an object can be determined by using a scale calibrated in pounds. Alternatively, you can convert the mass from other units such as kilograms to pounds using the conversion factor 1 kg = 2.20462 lbs.

3. What is the standard unit for velocity in English units?

The standard unit for velocity in English units is feet per second (ft/s).

4. Can kinetic energy be negative in English units?

No, kinetic energy cannot be negative in any unit system. It represents the amount of energy an object possesses due to its motion, so it is always a positive value.

5. How is kinetic energy used in real-world applications?

Kinetic energy is used in various real-world applications such as sports, transportation, and engineering. It helps in calculating the force required for a moving object to stop, determining the speed of a vehicle, and designing efficient machines like turbines and engines.

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