internal work

[gamarrapaul]

in the problem they give you V=44m/s, mass=.09 kg , and a vertical distance=18m
the problem states that a ball is shot straight down and at the distance 18m it encounters a sand bag the ball goes through the sand bag .5 m. they ask what is the internal work neglecting friction??????????
for this problem I have

-w=-mgh-.5mv^2

now I am confused for h do I use 18 m or 18.m ????

[Dick]

You use the distance over which gravity was doing work on the ball. Which is that?

[gamarrapaul]

the distance that gravity is doing work on the ball will be 18m ??

[Dick]

The distance gravity is doing work on the ball is the vertical distance that the ball moves. Gravity doesn't shut off inside the bag.

[gamarrapaul]

oh so the distance will be 18.5m I thought that .5 was the distance that the internal force is acting on the object Work = F*d