Robin Hood has to shoot an arrow at an apple that sits on a wall 400 meters away, at a height of 40 meters. He must shoot at an angle of 60 degrees. What must the initial velocity of the arrow be to hit the target? Assume he's shooting laying down on the ground, making the arrow's inital height to be 0, and use 10 m/s² as the value of gravity.

Question

Robin Hood has to shoot an arrow at an apple that sits on a wall 400 meters away, at a height of 40 meters. He must shoot at an angle of 60 degrees. What must the initial velocity of the arrow be to hit the target?  Assume he's shooting laying down on the ground, making the arrow's inital height to be 0, and use 10 m/s² as the value of gravity.

bobpursley · Answer

distance=vhorizontal*timeinair
400=Vcos60*t

hf=hi+vsin60*t-4.9t^2
40=0+Vsin60-4.9t^2

solve for t in the first equation, put tht into the second equation for t, and solve for V. It is likely to be a quadratic.
Notice I did not use 10m/s^2 for g, nowhere on Earth is that the value. I don't understand teachers who teach that...do they not think their students can work decimals on their calculators?