Question

The spin dryer of a washing machine rotating at 15 r.p.s. slows down to 5 r.p.s. after making 50 revolutions. Find its angular acceleration.

Answer 1

Given:

n₁ = 15 r.p.s
n₂ = 5 r.p.s
No. of revolution = 50
As, ω = 2πn
ω = 2π x 5 = 10π
Also, ω₀ = 2πn₀ = 2π x 15 = 30π

Angular displacement in/revolution = 2π
Angular displacement in 50 revolution = 2 x 50π
                                                              = 100π

Now, `ω^2 = ω_0^2 + 2alphatheta`  
  `(10pi)^2 = (30pi)^2 + 2alpha(100pi)`
                     `900pi^2 - 100pi^2`
`= -alpha` =____________________________
                              `200pi` 
`alpha = -4pi rad//s^2`
Also, `alpha = -12.56   rad//s^2`