# Angular acceleration, and revolution

#### keylostman

1. The problem statement, all variables and given/known data

A car engine accerlates from 1080rpm to 4800rpm in 12.5 seconds. Calculate the angular accleration, assumed constant, and the total number of revolutions the engine makes in this time

3. The attempt at a solution

angular acceleration (a) = (wf - wi) /(tf - ti)
(a) = (160 - 36) π / 12.5 = 31.15 rad/s^2

angle moved = θ = wi * t + 0.5 at^2
θ = 36 π *12.5 + 0.5 [124 π / 12.5 ] [12.5]^2
θ = 450 π + 0.5 [124 π] 12.5
θ = 450 π + 775 π = 1225 π
θ = [1225/2] [2π] = N[ 1 revolution]
N = numberof revolutions made = N = 1225/2 = 612.5

DID I DO THIS RIGHT?

#### PhanthomJay

Homework Helper
Gold Member
Yes. I suppose you didn't have to convert revolutions to radians when determining the angular acceleration, that is, you could have left it in rev/sec^2, although rad/sec^2 is the standard SI unit for angular acceleartion. Looks good.

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