Roller coaster

  • Thread starter ceday
  • Start date
  • #1
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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 doesnt give those variables

can anyone help?
thanks :)
 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
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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?
 
  • #3
11
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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
 
  • #4
LowlyPion
Homework Helper
3,090
4
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.
 
  • #5
11
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so would net force in the y direction = zero?

if it is zero, i dont think it would be solvable because we dont know the mass

wouldnt it be 0=mv2/r
 
  • #6
11
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ok, i got the answer but i used the net force=2mg
i still dont understand why this is so
 
  • #7
LowlyPion
Homework Helper
3,090
4
ok, i got the answer but i used the net force=2mg
i still dont understand why this is so
FNormal = ∑ F = Fcentrip - Fgravity

m*g = m*v2/r - m*g

2*m*g = m*v2/r
 

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