TPR Physics Mechanics Question (Help)

[Parcas]

There is a rotating cylinder ride at an amusement park so that when the ride achieves a speed of v, the floor can drop leaving the person suspended. The radius is 4m, coefficient of static friction is 0.5. What is the tangential speed required to suspend a 50 kg man?

Answer: 9m/s
To answer this problem (or problems similar to this), must I always assume that the normal force equals the centripetal force? And why does the normal force equal the centripetal force if the normal force is by definition opposite the gravitational force?? That connection didn't come to me right away and took me like 10 min to answer...

[Fn = Fc = (mv^2)/r. And to make the man suspend, the Ff = Fg. Since Ff = mu(s)*Fn, plug in and you get mg = mu(s)*(mv^2)/r. ]

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[swollcat]

They took circular motion off the new MCAT. I wouldn't waste another second on these types of problems. Check the official AAMC outline if you don't believe me.

 

[Parcas]

They took circular motion off the new MCAT. I wouldn't waste another second on these types of problems. Check the official AAMC outline if you don't believe me.

Oh, thanks for the heads up, I just checked and you seem to be right. That' a bit frustrating, I'll have to cross check everything I do instead of relying on TPR..

 

[ElectricNoogie]

Oh, thanks for the heads up, I just checked and you seem to be right. That' a bit frustrating, I'll have to cross check everything I do instead of relying on TPR..

In your previous example, yes the centripetal force is the normal force and the force of friction (Fn x coeff of frict) must fully counteract the weight of the person.

While the AAMC outline does not have UCM on it, you can still see this as an opportunity to test yourself on concepts the MCAT does say are fair game, namely equilibrium and Newtonian mechanics.

Do not be so quick to assume something not mentioned explicitly in the outline is "gone. The AAMC physics Q pack has a few pulley Qs in it and pulley are not mentioned anywhere in the outline at all. The pulley does serve as a way to test Newtonian equilibrium and work though, 2 topics that ARE listed.