The ball's kinetic energy would be
0.5*15*(70*5280/3600)**2 = 79,053.3 foot-pounds
or about 0.0298 kilowatt-hours.
“Let’s say a thug tosses a bowling ball at Amtrak 188, presently moving at 70 MPH. That would be 15LBS times 88FPS which would equal 1,742,000 foot pounds of energy.”
[Duke C’s initial approximation]
“The ball’s kinetic energy would be
0.5*15*(70*5280/3600)**2 = 79,053.3 foot-pounds
or about 0.0298 kilowatt-hours.”
[cynwoody’s approximation]
Neither used the correct amount for mass. In the English/American system of units, pounds are a measure of force, not mass.
f = ma (force equals mass times acceleration)
Inserting the actual figures, we get
15 pounds = m * 32.17 ft/sec**2 (gravitational acceleration at earth’s surface).
Solving for m, we find the mass of the bowling ball to be
m = f/a = 15/32.17 = 0.4663 pound-sec**2/ft (a unit commonly referred to as “slug” in engineering parlance)
Not sure where cynwoody found the conversion figure from mph to ft/sec but it is in error. The very first, most basic figure learned by aero engineers (and rocket scientists, and ballisticians) is 60 mph = 88 ft/sec (60 statute miles/hr = 316800 ft/hr / 3600 sec/hr = 88 ft/sec)
70 mph converts thus:
70 * 5280 ft/mile / 3600 sec/hr = 102.67 ft/sec
The equation to give us kinetic energy thus becomes
E = (0.4663 * (102.67)**2) / 2 = 2457 foot-pounds.