A man drives a go-kart around a circular track with a diameter of 50 m, at a rate of 314 m/minute. What is the frequency at which he circles the track in hertz (Hz)?

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

**Explanation**

B is correct. Hertz (Hz) is a measure of frequency with units of cycles per second, usually written as 1/sec. The number of cycles around the circle can be found by dividing the velocity by the circumference.

The circle circumference is (50 x pi) meters, or approximately 157 meters. The velocity of 314 m/min means that the driver completes 2 laps/min. The frequency in Hz is thus 2 laps/1 min x 1 min/60 sec = 1/30 Hz = 0.03 Hz.

- 0.0027 Hz, incorrect, This answer results from mistaking the formula for the area of a circle (which is pi times the square of the radius) with the formula for circumference (pi times diameter).
- 0.03 Hz, correct.
- 2 Hz, incorrect, This is laps/min rather than laps/second.
- 6.25 Hz, incorrect, This is the area divided by the velocity, with units of 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!

It has already been noted that the units in this question are labile, this shouldve been fixed by now. Lets get it together folks.

Hi there, thanks for reaching out! Are you referring to the use of pi in the question stem and explanation, and the potential confusion between the pi symbol and the “n” in nm (nanometers)? To clear up this confusion, we have revised the question to include units of meters/minute instead of pi*meters/minute. This should clear up that confusion. If you were referring to a different aspect of the question, or if you have any additional comments/insight, please let us know absolutely anytime.