Apparent weight

The passengers in a roller coaster car feel 50% heavier than their true weight as the car goes through a dip with a 20.0 m radius of curvature.
What is the car's speed at the bottom of the dip?

I'm stuck on this problem. I understand that at the bottom they feel 1.5 times heavier. Other than that I really don't know.

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 At the bottom of the curve their apparent weight is .5 normal, ie it has increased by 0.5. That's because there's an extra push upwards ion them, which is the "centripetal force". You know the expression for centripetal force - set this equal to 0.5weight, Rearrange to find v

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 Quote by NIZBIT I'm stuck on this problem. I understand that at the bottom they feel 1.5 times heavier. Other than that I really don't know.
The apparent weight, what they feel, is the force exerted on them by the seat of the coaster--also called the normal force. That's what is 1.5 times their real weight.

Analyze all the forces acting on the passengers and apply Newton's 2nd law. What kind of acceleration are they experiencing? (And how does that relate to their speed?)

Note: Centripetal force is not a force! It is the name for the net force on an object undergoing centripetal acceleration. If you were to list the forces acting on the passengers, "centripetal force" better not be on that list.