A tennis ball launcher uses a spring mechanism to project balls. The force to compress the spring an amount $z$ is given by $F = 100z + 5z^3$ , where $z$ is in meters and $F$ in newtons. If the spring is compressed 0.80 m, what speed will it give to a 0.057-kg tennis ball when released?

• A. $25 \mathrm{~m} / \mathrm{s}$
• B. $29 \mathrm{~m} / \mathrm{s}$
• C. $34 \mathrm{~m} / \mathrm{s}$
• D. $40 \mathrm{~m} / \mathrm{s}$

Answer: (C)