How Do You Calculate Angular Acceleration from RPM?

[J-Fly]

A 61 cm diameter wheel accelerated uniformly about its center from 120 rpm to 280 rpm in 4.0 seconds. Determine the Angular acceleration

So I converted the 120 and 280 rev per min to radians per s with 45238.93 rad/s and 105557.51 rad/s and used them as angular velocity final and initial. then I subtracted the final from the initial and divided it by the time (4 sec)

Equation used angular acceleration (fish) = change in angular velocity/time

Answer gotten: 15 x 10³ rad/s² with sig figs.

on the answer sheet= 4.2 rad/s²

 

[gneill]

Can you show your calculations for converting the given rpm values to radians per second? Your values look rather high.

 

[Aceix]

er

A 61 cm diameter wheel accelerated uniformly about its center from 120 rpm to 280 rpm in 4.0 seconds. Determine the Angular acceleration

So I converted the 120 and 280 rev per min to radians per s with 45238.93 rad/s and 105557.51 rad/s and used them as angular velocity final and initial. then I subtracted the final from the initial and divided it by the time (4 sec)

Equation used angular acceleration (fish) = change in angular velocity/time

Answer gotten: 15 x 10³ rad/s² with sig figs.

on the answer sheet= 4.2 rad/s²

There is a problem with your conversion. Note that 1rpm=(2pi*1)/60 rad/s