Calculating Speed of Roller Coaster Car at Top of Loop-the-Loop

[ceday]

Homework Statement

The normal force equals the magnitude of the gravitational force as a roller coaster car crosses the top of a 60m diameter loop-the-loop.

Homework Equations

What is the car's speed at the top?

The Attempt at a Solution

hello, this problem doesn't give much information
would normal force be pointing down?

so Fnet= ma=mv^2/r but its doesn't give those variables

can anyone help?
thanks :)

 

[LowlyPion]

Don't you have all you need?

Draw a diagram.

m*g down and mv²/r up

But it says the Normal force is still m*g

If the net force must be m*g and you have m*g acting down against the centripetal force, what must the centripetal force be?

 

[ceday]

Is the net force in the y direction zero?

does the centripetal force = 2mg since normal and gravity both point downward?

im lost since this coaster is upside down

 

[LowlyPion]

Is the net force in the y direction zero?

does the centripetal force = 2mg since normal and gravity both point downward?

im lost since this coaster is upside down

Not lost at all.

The centripetal force is 2*m*g.

 

[ceday]

so would net force in the y direction = zero?

if it is zero, i don't think it would be solvable because we don't know the mass

wouldnt it be 0=mv²/r

 

[ceday]

ok, i got the answer but i used the net force=2mg
i still don't understand why this is so

 

[LowlyPion]

ok, i got the answer but i used the net force=2mg
i still don't understand why this is so

F_Normal = ∑ F = F_centrip - F_gravity

m*g = m*v²/r - m*g

2*m*g = m*v²/r