Final answer:
The ball must be thrown horizontally at an elevation angle of 0 degrees to achieve maximum height.
Step-by-step explanation:
To find the angle θ0 at which the ball must be thrown to achieve maximum height, we need to determine the elevation angle that gives the highest value for the expression v0/2(1+cosθ0). In this case, v0 is the initial velocity when the ball is thrown horizontally. To maximize the expression, we need to find the value of θ0 that maximizes the cosine function.
To find the maximum value of cosθ0, we know that the cosine function has a maximum value of 1 when θ0 is 0 degrees. Therefore, the ball must be thrown at an elevation angle of 0 degrees (horizontally) in order to achieve maximum height.