a grinder turns at 4500rpm. how many revolutions does it make in 1 second?

1 minute = 60 seconds, so to find RPS, you can divide the RPM by 60. $$ RPS = RPM / 60 $$ $$ RPS = 4500 / 60 $$ $$ RPS = 75 $$ So, the grinder makes 75 revolutions in 1 second