Question 1154319
[ mi/hr ] x [ ft/mi ] x [ in/ft ] = [ in/hr]
[ in/hr ] x [ hr/min ] = [ in/min ]
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{{{ ( 55/1 )*( 5280/1 )*( 12/1 ) = 3484800 }}} in/hr
{{{ ( 3484800/1 )*( 1/60 ) = 58080 }}} in/min
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In 1 revolution the wheel lays down 1 circumference
{{{ C = 2*pi*21 }}}
{{{ C = 2*3.14159*21 }}}
{{{ C = 131.9469 }}} in
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[ in/min ] / [ in/rev ] = [ rev/min ]
{{{ 58080 / 131.9469 = 440.1771 }}} rev/min ( the rpms )
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[ rev/min ] x [ rad/rev ] = [ rad/min ]
{{{ 440.1771*2*3.14159 = 2765.714 }}} rad/min ( the angular speed )
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check the math & get a
2nd opinion if needed