Answer
(a) $5.7m$
(b) height change is independent of the mass.
Work Step by Step
(a) According to law of conservation of energy
$\frac{1}{2}mv_i^2+0=\frac{1}{2}mv_f^2+mgy_f$
This can be rearranged as:
$y_f=\frac{1}{2g}(v_i^2-v_f^2)$
We plug in the known values to obtain:
$y_f=\frac{(16)^2-(12)^2}{2(9.81)}$
$y_f=5.7m$
(b) We know that the height change does not depend on the mass. That is why it is not necessary to know the mass of the tennis ball.
