21) For this problem, we are going to want to find the projectile's launch angle. We are told that the minimum speed of the projectile is 15.0 m/s and occurs 1.94 seconds from the launch.
Let's figure out when a projectile travels at its minimum speed.
Since we can assume negligible air resistance, v[x] is a constant. Thus, we can find our minimum speed when the magnitude of v[y] is minimized. This happens at the max-height, where v[y] is 0 m/s.
From this point, knowing acceleration due to gravity, the time it takes to reach max-height, and v[y] at max-height, we can find the initial vertical velocity.
Finally, since we have the initial velocity in the x-direction and y-direction, we can use basic trigonometry to find the angle of incline.
Answer: B
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