Work is the joules of energy expended in accomplishing the stroke specified by the initial and final ball speeds, and the other constraints in the benchmark conditions. See the accompanying remarks.
Power is the rate of doing work, joules per second, and one horsepower is 746 joules per second (watts), or 550 foot pounds per second.
A complete description of the variables used in the derivation follows at the end.
Applying Conservation of Angular Momentum:
Iw1 + dbs1 = Iw2 + dbs2
Note that this involves the same assumption as in the Torque derivation about the restoring torque of the player being a non-impulsive force that may be disregarded in the conservation equation. Since d and I are in centimeters (see the Torque derivation):