Why Use Angular Acceleration Instead of Radial?

[DaveTan]

Homework Statement

The cosmoclock 21 Ferris Wheel in Yokohama City, Japan, has a diameter of 100m. Its name comes from its 60 arms, each of which can function as a second hand (so it makes one revolution every 60.0s).

a) Find the speed of the passengers when the Ferris wheel is rotating at this rate [No problem]
b) A passenger weighs 882N at the weight-guessing booth on the ground. What is his apparent weight at the lowest point of the ferris wheel?

Homework Equations

d = vt
a_rad = v^2.r
w = mg

The Attempt at a Solution

I have no problem with part a.

distance = 2pi r = 314.1m
velocity = 314.1/60 = 5.235m/s

It is part b where I get confused. I get it right till the step to use acceleration. I use radial acceleration and get it wrong, googled the question and someone used angular acceleration. I used his angular acceleration value and my answer was correct. But I am wondering why use angular acceleration instead of radial?

Weight on ground = 882N
Mass = 89.9 kg

F = ma
N_b - mg = ma
N_b = m (a +g)

*This is the part where I use radial acceleration
a = v²/r
a = 0.1745m/s²

N_b = 89.9 (0.1745+9.81)
N_b = 897.6N

 

[BruceW]

Hi, welcome to physicsforums :)
the equation you are using a=v²/r is the correct one. And your value for the velocity is good. I think you made a mistake in doing the calculation v²/r. what values did you use? Remember you should be using radius, not diameter.

 

[DaveTan]

Hey Bruce! Haha you are right! Opps! Thank you!

 

[BruceW]

no worries! glad to help :) Your method was good.