How Do You Calculate the Launch Angle and Velocity of a Cannonball?

[wisper]

Ok, I am having a hard time understanding how to approach this problem the correct way interms of physics.

A cannon shoots a ball going a total distance of 79.5 meters, clearing a wall 67.5 meters away from where it was initially shot. The wall is 17.58 meters high, what is the allowable launch angle and velocity? Assume gravity is 9.81 meters per second squared.

 

[naul]

canon

draw the projectile
list all the equations of a projectile
try to calculate the maximum heigt
try to find range

 

[HallsofIvy]

Write down the formulas for distance and height of a projectile depending on angle and initial speed. You know that the range (distance until the height is 0 again) is 79.5 and that the height 67.5 meters away is at least 17.58 meters. That gives you two equations for angle and speed.