Solving the Stopping Force of an Arrow Shot into Hay

[askthefool]

An arrow of mass 20 grams is shot horizontally into a bale of hay with a velocity of 60 m/s. It penetrates a debpt of 20 CM before stopping.

What is the average stopping force acting on the arrow?


I've been doing

W = -F*D
W = -(ma)*d

I'm finding a by using a kinematic equation, v (final ) ^2 = v (initial ) ^ 2 + 2 a (delta) x.

The answer I'm getting is 360 N, but that is not the correct answer. Any ideas?

 

[askthefool]

I'm an idiot. Never mind. I misread to work done by the stopping force. 180 is the right answer for those that care. There is no need for work at all, just a simple F = ma problem.

 

[Locrian]

If misreading the question makes one an idiot, I'm an idiot many times over for trasngressions as an undergrad :(