# Homework Help: Circular motion of a clock

1. Jan 8, 2008

### lil-devil

The problem statement
a) for a clock with minute hand 20 cm long find the average accelration of the hand as it moves from the 4 position to the 8 position

b)an amusement ride is a rotating cylinder where the person is plastered to the inside wall as the ride speeds up and the floor drops away. if the cylinder is 6.6m across and turns 10.362 times in 21.5s what coeffient of friction is required to keep a person with mass 55kg from slipping down

The attempt at a solution
a)
data given
40min-->2400 secs (40 min since 4-8=40min)
20cm-->0.2m
1hour-->3600 sec

so first i drew a circle with tangents from 4 and 8 labling one tangent v1 and the other v2
and used this equation to find v
v=(4pi^2r)/(t^2) then from there on im not sure how you get acceleration since the other formula i can think of is a=(deltaV)/(delta t)
but i can't use that formula since i don't have the differences in velocity so im not sure where to go from that

b)
givens
freq=0.48 -->(10.362/21.5)
got a fdb

^friction
|
Fn<--o
|
v mg

so fnety=f-mg
since the guy isn't falling
fnety=0
therefore f=mg
since
f=mewFn
mg=mewfn
so theres 2 unknowns, how do you find Fn?