A tennis ball bouncing on a hard surface compresses and then rebounds. The details of the rebound are specified in tennis regulations. Tennis balls, to be acceptable for tournament play, must have a mass of 57.5 g. When dropped from a height of $2.5 \mathrm{m}$ onto a concrete surface, a ball must rebound to a height of $1.4 \mathrm{m} .$ During impact, the ball compresses by approximately $6 \mathrm{mm}$.
How fast is the ball moving when it hits the concrete surface? (Ignore air resistance.)
A. $5 \mathrm{m} / \mathrm{s}$
B. $7 \mathrm{m} / \mathrm{s}$
C. $25 \mathrm{m} / \mathrm{s}$
D. $50 \mathrm{m} / \mathrm{s}$