**units of measure**

... Now the kinetic energy of motion at 70 mph is (.5mv^2) = 510682 lb-ft...

In any system of units, the product of force and distance can be torque (moment of force), or energy, depending on context. For instance, in SI the units of torque are N⋅m, while the unit of energy is kg⋅m2/s2, or joule... which is also N⋅m. To keep these straight, the usual convention in the old units is to put the force unit first for torque (lb-ft), and the distance unit first for energy (ft-lb), so arguably kennybobby should have used ft-lb... but I don't think there's a consistent rule. Certainly in this context it is clear that the quantity is energy.kinetic energy is measured in joules. lb-ft is a measure or torque, not energy.

The fact that ft-lb is a unit of energy is demonstrated as kennybobby continued to show that the rate of change of energy is power... including that a "horsepower" is defined as 550 lb-ft/sec (just as a watt is a J/s or N⋅m/s or kg⋅m2/s3For a first order power estimate take the kinetic energy divided by your acceleration time, let's assume 0 to 70 in 13 seconds.

This gives a power of 39283 lb-ft/sec, a horse can pull 550 pounds over a distance of one foot in one second, so divide by 550 to get about 72 horsepower required for acceleration.

Yes, that avoids the unit conversion constants, but the physics is the same regardless of the system of units.Learn SI units, it makes the calculations a lot simpler.