Answer
a) See the detailed answer below.
b) See the figure below.
c) $v_{0y}=17.2\;\rm m/s$
Work Step by Step
a) A tennis ball was fired vertically upward at $v_{0y}$ and it moved up until it reached a height of 10 m. At this moment its velocity was 10 m/s. Find its initial velocity.
b) See the figure below.
c) Solving for $v_{0y}$;
$$v_{0y}=\sqrt{10^2+(2\cdot 9.8\cdot 10)}=\color{red}{\bf 17.2}\;\rm m/s$$
