TBR forces and torque

[deleted783484]

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The question asks: "If a person starts at the rim of a spinning platform and is pushed radially toward the central axis by a moving exterior wall, then what happens to the normal force felt by that person due to the wall?"

Answer is: "It decreases, since r decreases"

I used a= v^2/r but TBR used w^2*r. How do we know which to use? And are they using newton's second law Fnet= ma to say that since a decreases Fn decreases as well?

Thank you!

 

[Neuroplasticity]

In ratio kinds of problems, you want to find a relation between your two variables where they are the only variables changing in that equation.

In F=m*(w^2*r), the object's mass and is angular velocity are constant.
In F=m*(v^2/r), the mass is constant, but the tangential speed, v, is changing, so it is harder to know the relation between F and r.

Tangential speed changes because when the object is farther from the center, it travels a farther distance in the same time than when it is closer to the center.