Helicopter blades withstand tremendous stresses. In addition to supporting the weight of a helicopter, they are spun at rapid rates and experience large centripetal accelerations, especially at the tip.

- Calculate the magnitude of the centripetal acceleration at the tip of a 4.00 m long helicopter blade that rotates at 300 rev/min.
- Compare the linear speed of the tip with the speed of sound (taken to be 340 m/s).

a) $3950 \textrm{ m/s}^2$

b) $37 \%$

### Solution video

# OpenStax College Physics, Chapter 6, Problem 15 (Problems & Exercises)

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## Comments

I'm sort of confused, i thought a unit such as revolutions per min would be considered a unit of frequency and not angular speed.

Hi parm, I can see what you mean. The dimensions are the same - a counting (dimentionless) unit divided by time. A revolution can be thought of as "2 pi radians" or "360 degrees", so rpm is measuring the number of times the object rotates through 360 degrees per minute. Maybe rephrasing rpm that way helps show the connection to angular speed, which is likewise "angle per time".

All the best,

Shaun