Efficiency of energy transformation on a slide

[gungo]

Homework Statement

Students used a speed gun to measure the final speed of slider at the bottom of the slide. They measure the height difference between the top and bottom of the slide to be 3.0 m.
If the speed of a slider at the bottom of the slide is 5.0 m/s, what is the efficiency of the energy transformation?

Homework Equations

mgh1+1/2mv^2=mgh2+1/2mv^2
efficiency=Eout/Ein x100

The Attempt at a Solution

the masses of :mgh1+1/2mv1^2=mgh2+1/2mv2^2 cancel out, so I'm left with
gh1+1/2v^2=gh+1/2v^2
3(9.8)+1/2v1^2=1/2(5)^2
When I isolate v1^2, I get a negative number which wouldn't work because I can't get the square root of it to find v. But after finding v, what would I do?

 

[haruspex]

mgh1+1/2mv^2=mgh2+1/2mv^2

That equation assumes no losses.

3(9.8)+1/2v1^2=1/2(5)^2

The 5 in there is for the case where there are losses, so the equation does not apply.