Mechanical energy into thermal energy

[anna sung]

Homework Statement

the roller coaster is 94.5m high at its highest point. what is the maximum possible speed of the roller coaster? the roller coaster's actual maximum speed is 4.1m/s.what percentage is lost to thermal energy due to friction?

Homework Equations

Wnc= Efinal-Eintial
the part i didnt get is highlighted in red.
please help me

The Attempt at a Solution

Wnc= Efinal- Eintial
Efinal= Ek
Einitial=Eg
after i got the numbers i said (Wnc/Einitial)*100 to get the percentage. but it did not get me to the answer.
the answer on the book is = 8.9%
and its maximum speed is = 43.1 m/s

 

[panchoman]

divide Wnc by the energy that it should've had (with the 43.1 m/s velocity, .5m(43.1)^2)
and then multiply by 100