A man drives a go-kart around a circular track with a diameter of 50m, at a rate of 100πm/minute. What is the frequency at which he circles the track in Hertz?

- 0.0027 Hz
- 0.03 Hz
- 2 Hz
- 6.25 Hz

**Explanation**

1030. Hz is a measure of frequency with units cycles/second usually written as 1/sec. The number of cycles around the circle is the velocity/circumference.

The circle circumference is 50πm. The velocity of 100πm/min means that the driver completes 2 laps/min. The frequency in Hz is 2 laps/1min x 1 min/ 60 sec=1/30 Hz=0.03 Hz.

- 0.0027 Hz, incorrect, This answer results from using the distance as π(25m)2=625πm.
- 0.03 Hz, correct.
- 2 Hz, incorrect, This is laps/min rather than laps/second.
- 6.25 Hz, incorrect, This is the area/velocity with units 1/min rather than 1/sec.

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This answer cannot be correct…in the question stem, it states that the diameter of the circle is 50 m. That would mean that the circumference is 157.08 m…or 157 x 10^9 nm.

Hi Amy, thanks for the question! That’s a pi symbol, not the “n” for nanometers. So your calculation of 157.08 m was exactly correct – we just wrote it out as 50(pi) meters. I hope this clears up any confusion!