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Math Help - [SOLVED] linear/angular speed?

  1. #1
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    [SOLVED] linear/angular speed?

    If a rocket car with 20 inch radius tires brakes the sound barrier (a speed in excess of 760 miles/hour), what is the angular speed of the wheels in revolutions/second?

    ok i am totally lost.....all i know is one revolution would probably be 40pi inches because that the circumfrence of the circle...and i thought i probably have to use the formula v=rw (v=linear speed, r=radius and w=angular speed)

    so i started with

    760mi/hr = 20w but im confused with the units??? i dont know if i even started it off right ???

    thank you(:
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  2. #2
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    Linear/angular speed

    Hello desperate_on_sunday_night
    Quote Originally Posted by desperate_on_sunday_night View Post
    If a rocket car with 20 inch radius tires brakes the sound barrier (a speed in excess of 760 miles/hour), what is the angular speed of the wheels in revolutions/second?

    ok i am totally lost.....all i know is one revolution would probably be 40pi inches because that the circumfrence of the circle...and i thought i probably have to use the formula v=rw (v=linear speed, r=radius and w=angular speed)

    so i started with

    760mi/hr = 20w but im confused with the units??? i dont know if i even started it off right ???

    thank you(:
    Use v = r\omega if \omega is measured in radians. Here, stick to your first idea, and work with the circumference of the tire, which is 40\pi inches.

    So, in 1 revolution, the car moves forward 40\pi inches = 125.68 inches.

    And we know that in one hour, the car would move forward 760 miles. So in one second it moves forward 760 \div 3600 miles, or 760 \times 5280 \times 12 \div 3600 inches, which = 13376 inches.

    So, how many revolutions do we need to make this many inches? Answer: 13376 \div 125.68 = 106.5. So there's your answer: just over 106 revolutions per second.

    Grandad
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