A record player’s needle is 6.5cm from the center of a 45-rpm record. What is the velocity of the needle?

4 Responses to “A record player’s needle is 6.5cm from the center of a 45-rpm record. What is the velocity of the needle?”

1. 
   #1
   opal1331
   February 5th, 2010 8:57 pm

   The needle doesn’t have any velocity, it’s stationary, only the record is moving.
   References :

2. 
   #2
   rick994
   February 5th, 2010 9:34 pm

   Technically the needle doesn’t have a velocity with respect to earth because it doesn’t move. The record spins while the needle sits. Does the question ask what the relative velocity of the needle is with respect the the record? Could be a trick question.
   References :

3. 
   #3
   bob shark
   February 5th, 2010 10:23 pm

   Circumference is Pi times diameter
   Diameter is raidus time 2 = 13CM
   13 x 3.1416 = 40.84 cm circumference.
   40.84 x 45 rpm =1,837.836 Cm per min or 18.38 meters per min
   References :

4. 
   #4
   to_700million_idiots
   February 5th, 2010 11:04 pm

   ignore them … you meant relative velocity

   why do you find this hard?

   the radius is 6.5
   so the perimeter of that circle is 2 Pi R
   and it covers that distance 45 times in a minute

   Dist=2×3.142×6.5
   Time = 60/45
   Velocity = D/T

   so we have 13 x Pi x 45 / 60 = 30.63 cm/second

   (or 18.378 m/min 0r 0.3063 metres/second)
   References :

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