The minute hand of a large clock is 0.50 m long. (a) calculate its linear speed at its tip in meters per second. (0.000873 m/s)
(b) calculate the centripetal acceleration of the tip of the hand. (1.52 x 10-6 m/s2)

The rotational speed of the minute hand is 360 degrees in one hour or:
ω = 2π rad/3600 sec
or 
ω = 0.001745 rad/sec

To convert this to linear speed, we use the formula:
v = rω

Substituting the given values:
v = 0.5 (0.001745) = 0.000873 m/s

For the centripetal acceleration:
a = v^2/r
a = (0.000873)^2 / 0.5
a = 1.52 x 10^-6 m/s^2

The magnets are probably damaged or there not strong enough to attached to the refrigerator