You are using high-speed motion pictures at 3200 frames/second to analyze a projectile launched from a toy gun at a nearly vertical angle. The projectile has 20 g and is 5 cm long. You generate the graph shown below using data from the motion pictures. From the graph, when is the acceleration of the projectile zero? 

• A. t ≥ 0 ms
• B. t ≥ 150 ms
• C. t ≥ 75 ms
• D. t ≥ 325 ms
• E. The acceleration is never equal to zero

Answer: (B)