Australian Intermediate Maths Challenge Stage I3 - Factory Bells?

[Tyrome]

In his factory, Max needs an alarm that rings every hour. He pulls apart an old bicycle and builds a machine using the bicycle chain and one of the sprocket wheels. He breaks the chain, hangs it over the wheel and attaches a bell to each end as shown.

http://i914.photobucket.com/albums/ac343/tyromeisflash/drawing008.jpg

Max attaches the motor that turns the wheel clockwise for exactly one hour then anti-clockwise for exactly one hour, both at the same constant rate.

He positions the center of the wheel on the wall so that at 12 noon the bell on the left hits the floor and rings. This process continues alternately every hour.

A) At 12.10 p.m. the difference in height between the 2 bells is 80 cm. How far off the floor is the left bell at 3 p.m.?

B) The diameter of the sprocket wheel (to the center of the chain width) is ten centimetres. How many revolutions (rounded to 2 decimal place) does the wheel make each hour?

[Unregistered]

it is 120 cm because
60 min=120
50 min=80
40 min=40
30 min=0 (this is when the both bells are level)
20 min=40
10 min=80
00 min=120