What Elevation Angle Clears the Wall and Hits the Target?

[rsmseys]

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.

 

[The legend]

and how did you reach your answer?

According to PF rules no solns can be given... just help or advice.

 

[rsmseys]

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.

 

[zgozvrm]

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.