a roller coaster at an amusement park is at rest of top of a 30m hill (point A). the car starts to roll down the hill and reaches (point b), which is 10 m above the ground, and then rolls up the track to point C, which is 20 m above the ground.

- A student assumes no energy is lost, and solves for how fast is the car moving at point C using energy arguements. What answer does he get?

Question

a roller coaster at an amusement park is at rest of top of a 30m hill (point A). the car starts to roll down the hill and reaches (point b), which is 10 m above the ground, and then rolls up the track to point C, which is 20 m above  the ground. 

- A student assumes no energy is lost, and solves for how fast is the car moving at point C using energy arguements. What answer does he get?

anonymous · Answer

use potential and kinetic energy equations.
Set them equal to each other
Then you can cancel out mass

curry · Answer

I got 10rad2 but the answer is 20 m/s. I got 20m/x at point B not point C. For point C, I got 10rad2 = rad 200

anonymous · Answer

you only have to find the energy at point C.
the kinetic energy at point C will be the same as the potential energy in the difference of height from point A to point C.
does that make any sense?

anonymous · Answer

I don't have the actual answers.

anonymous · Answer

yet

curry · Answer

it does, but the answer still shouldn't be 20m/s

anonymous · Answer

and I don't think it is 20m/s at point B

anonymous · Answer

it's not 20 m/s
mgh=mv^2
gh=v^2

curry · Answer

KE = 0.5mv^2

anonymous · Answer

oh. yes. thank you.

anonymous · Answer

2gh=v^2

curry · Answer

in which case, I'm right? and the book is wrong?

anonymous · Answer

yes

curry · Answer

kk thanks!! :D