Help with this Ferris wheel rotational physics problem please

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SUMMARY

The discussion centers on solving a rotational physics problem involving a Ferris wheel, specifically calculating the mass of an object based on centripetal and gravitational forces. The user initially calculated the mass as 7.9 kg but recognized a sign error in their equations. The correct approach involves ensuring that both centripetal acceleration and gravitational acceleration are treated consistently in terms of direction. The user corrected their equation for acceleration at the bottom of the wheel, leading to a more accurate understanding of the forces involved.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with centripetal acceleration concepts
  • Basic knowledge of gravitational force calculations
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Study the principles of centripetal force in circular motion
  • Learn about gravitational force calculations in physics
  • Explore common sign conventions in physics problems
  • Practice solving rotational dynamics problems involving forces
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This discussion is beneficial for physics students, educators, and anyone interested in understanding the dynamics of rotational motion and force calculations in real-world applications.

takelight2
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Homework Statement
A woman rides on a Ferris wheel of radius 16m that maintains the same speed throughout its motion. To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it. When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale reading versus time. (Figure 1) Note that the graph has a minimum value of 510N and a maximum value of 666N. The acceleration due to gravity, g=9.80m/s2.
Relevant Equations
What is the woman's mass?

Express your answer in kilograms.
So this is what I've attempted:

666 = m*a1
510 = m*a2

a1= ac + 9.8
a2= ac-9.8

666 = m(ac+9.8)
510 = m(ac-9.8)

666 = m*ac + m*9.8
510 = m*ac - m*9.8

156 = 2m(9.8)

m = 7.9 kg (which seems very wrong haha)

any ideas?? I thought my reasoning was okay, since I considered that at the top of the wheel (where weight is max), both the centripetal acceleration and the gravitational acceleration point downward, and at the bottom (weight is min) they point in opposite directions so they must subtract.. What am I doing wrong here?
 
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takelight2 said:
What am I doing wrong here?
You are making a sign error. The 510 N and 666 N are in the same direction as g
 
BvU said:
You are making a sign error. The 510 N and 666 N are in the same direction as g

Oh ok. So then i can just change a2= -ac +9.8, making downward positive.

Ok thanks a lot.
 

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