-Unsolved-Work, Energy problem and friction

[bulbasaur88]

----Unsolved----Work, Energy problem and friction

EEEK I already posted this problem, but I cannot find it anymore! SO here it is again!

A student, starting from rest, slides down a water slide. On the way down, a kinetic frictional force (a nonconservative force) acts on her. The student has a mass of 70 kg, and the height of the water slide is 11.3 m. If the kinetic frictional force does -7.6 × 10^3 J of work, how fast is the student going at the bottom of the slide?

Vo = 0 m/s
m = 70 kg
Ho = 11.3 m
Hf = 0 m
Wnc = -7.6 x 103 J

Wnc = 0.5m(Vf2 -Vo2) + mg(Hf-Ho)

-7.6 x 103 = 0.5(70)(Vf2) + 70(9.8)(11.3)

Vf = 20.9 m/s

A person on physicsforum tried to help me but it was the wrong answer, and I only have one chance left to answer it correctly on the computer software. please help?

 

[Doc Al]

Here's the thread you already have going: https://www.physicsforums.com/showthread.php?p=3548423

(Don't create multiple threads for the same problem.)