Potential Grav. Energy to Kine. Energy Problem

[iamtrojan3]

Homework Statement

On a roller coaster ride the total mass of the cart - with passengers included - is 280 kg. Peak K is at 46.0 m above the ground, peak L is at 21.5 m. The speed of the cart at K is 17.1 m/s, at L it is 12.8 m/s. How much energy is lost due to friction between the two peaks?

Homework Equations

Ke = 1/2mv^2 = mgh

The Attempt at a Solution

I tried finding the Ke at the 2 different points and subtracting.. it didn't work .
then i tried with the mgh and subtracted it, and it still didn't work.
So i guess I'm confused on which of the given data i should use.

Thanks a lot!

 

[Doc Al]

Compare the total energy (KE + PE) at the two points.

 

[iamtrojan3]

i see. I got 85000, which was right.
Thanks again