What Elevation Angle Clears the Wall and Hits the Target?

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Homework Help Overview

The problem involves a projectile motion scenario where a projectile is launched with an initial speed of 20 m/s to hit a target located 28.9 m away, while needing to clear a wall that is 10 m high positioned halfway to the target. The objective is to determine the appropriate elevation angle for the launch.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations leading to different elevation angle results, with one participant asserting an angle of around 44 to 45 degrees and another suggesting it should be closer to 65 degrees. There are questions about the methods used to arrive at these angles and the implications of clearing the wall versus hitting the target.

Discussion Status

The discussion is ongoing, with participants providing insights into their calculations and questioning the assumptions made in the problem setup. Some guidance has been offered regarding the need to reconsider the trajectory in relation to both the wall and the target.

Contextual Notes

Participants are navigating the constraints of homework rules that prohibit direct solutions, which influences the nature of the guidance and discussion. There is also a noted discrepancy in the results that prompts further exploration of the projectile's path.

rsmseys
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Homework Statement



A projectile, initial speed v = 20 m/s is supposed to hit a target D = 28.9 m away. However an H = 10 m high wall is placed halfway between the launching point and the target. What is the appropriate elevation angle? (in degrees).

Homework Equations



http://en.wikipedia.org/wiki/Equations_of_motion#Equations_of_uniformly_accelerated_linear_motion

The Attempt at a Solution



I got the answer of around 44 to 45 degrees. The correct answer is said to be closer to 65 degrees. Any help in clarifying which answer is right would be helpful, along with solutions. Thanks.
 
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and how did you reach your answer?

According to PF rules no solns can be given... just help or advice.
 
v = at
20sin(x) = 9.8t
20sin(x) / 9.8 = t
s = 1/2(u +v)t
10 = 1/2 * (20sin(x))*(20sin(x))/9.8

Solving for x, the answer for x (the angle) is 44.427 degrees.
 
Not quite, but you're on the right track.

Work it backwards with your result and you'll see that although you just cleared the wall, you missed the target by nearly 12m.
 

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