Double Checking a Bicycle Downhill Homework Problem

[Aikenfan]

Homework Statement

I wasn't sure if i was doing this problem correctly, if anyone could double check for me, that would be great!
You ride your bicycle down a hill. Your total mass is 40 kg. At the top of the hill, your
speed is 5 m/s. The hill is 20 m high and 200 m long. If the force of friction is 20 N, what is
your speed at the bottom of the hill?

Homework Equations

The Attempt at a Solution

Top =
KE = 1/2 m v ^2
KE = 1/2 (40) (5)^2 = 500

PE = mgh
(40) (9.8) (20) = 7840

W = Fd
(20)(200)= 4000

7840 - 4000
=3840

3840 + 500 = 4340 = 1/2 (40) v ^2
divide both sides by 20
take the square root, and got 14.7 as my answer...

 

[Dick]

Looks ok to me. Though I'd be more careful about putting units on things.