Question

A fan is marked 900 rpm . What is the frequency of movement

Answer 1

rotation per minute representing angular speed-ω

Frequency is always in seconds
that's why we have to convert rpm(rotation per minute) to rps(rotation per second)

$ω = 900 \\ in \: seconds \\ \\ ω = \frac{900}{60} \\ ω = 15 \\ \\ ω = 2\pi \: f \\ f - frequecy \\ 15 = 2\pi \: f \\ f = \frac{15}{2\pi}$

$\fcolorbox{yellow}{red}{frequency\: is \:2.38}$