225 feet
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225 feet is a very vague and most importantly, incorrect answer.
If you know for sure you are throwing 55mph off of a mound, then during a long toss session if you throw a Baseball around a 45-50 degree angle you should be able to reach around 150 feet. 225 feet translates into about 73mph thrown at a 45 degree angle. This is also for the fact that the elevation at which you are is close to sea level and if there is little to no wind.
-R
The equivalent of an 80mph pitch from 47ft at 54ft is 54/47*80 = 91.9 mph.
About 120, if I recall correctly, though it could be less.
6.1 mph = 8.95 feet / second.
2,200 feet per second is 1,500 mph
15 mph = 22 feet per second
40 mph = about 58.6 feet per second.
1,200 feet per second = 818.2 mph
Five mph equates to about 7.333 feet per second.
350 feet per second = 238.64 mph
69 mph is 101.2 feet per second.
55 mph = 80.6666 feet per second
1,000 mph = 1,466.66 feet per second