Question on Normal Force, Gravity, and Tension

[collegelife101]

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I'm really stuck on one of the physics practice passages from TPR. The passage shows an amusement park ride which consists of a carriage attached to a mechanical arm. This arm spins the carriage around in a full circle.

One of the question asks: With its carriage full, the second ride goes through the top of its swing. What is the value of the normal force if its speed is 20 m/s?

I understand the logic behind how to solve the problem, but the solution only includes the normal force and gravity in the centripetal force. What about the tension in the mechanical arm though? Why was that not included?

Thanks!

 

[syoung]

Tension in the mechanical arm would be the centripetal force.

If we have a free body diagram...

At the top there should be the Tension towards the circle (centripetal force), W down and N up. N is the apparent force felt by the carriage.
T = mg - N
Fc = mg - N

At the bottom there should be Tension towards the circle, W down and N up.
T = N - mg
Fc = N - mg

 

[NextStepTutor_2]

Hey Collegelife,

Good question. Just an add on to syoung's answer. Remember that centripetal force is a NET force, that causes a spin. What this means is that centripetal force can be equivalent to the effect of multiple forces.

Hope this helps!

 

[Teleologist]

What's the difference between centripetal and radial force?