Impossible Roller Coaster question (for me anyway)

[scolaiw]

Question in this link (includes diagram): http://b.imagehost.org/view/0431/photo"

I am assuming it require Energy equations

The attempt at solution = Fail

Please HELP!

 

[Doc Al]

I am assuming it require Energy equations

Definitely.

The attempt at solution = Fail

For some reason, you set KE = GPE. Instead, consider the total energy at any point. That total energy doesn't change. Write an equation expressing that fact.

 

[scolaiw]

I still don't get it... How can you do so, without knowing the mass of "cart"? Where does all the velocities factor into this?

 

[scolaiw]

How come no one replies...?

 

[Doc Al]

I still don't get it... How can you do so, without knowing the mass of "cart"? Where does all the velocities factor into this?

Call the mass of the cart 'm'. It doesn't matter and will drop out of any calculation.

Did you write an expression for the total mechanical energy of the cart?

 

[scolaiw]

Yeah that's what I don't get, how can you get the total mechanical energy from so little information?

Thanks so far btw.

 

[Doc Al]

Yeah that's what I don't get, how can you get the total mechanical energy from so little information?

You don't need the actual numerical value for the total energy. (You don't have the mass, afterall.) All you need to find is the height of point Y and you are given all the information you need to do that.

Compare the total energy at point X to the total energy at point Y.

 

[scolaiw]

Ok I've exhausted just about all of my effort and still not getting it. Physics is hard for 17 year old :P.

Can you please tell me the first line of the equation?

 

[scolaiw]

I am thinking 0.5mv^2 + mgh = 0.5mv^2 + mgh and solving for second h.

 

[Doc Al]

I am thinking 0.5mv^2 + mgh = 0.5mv^2 + mgh and solving for second h.

Exactly!