Answer:
69.970 rev
Explanation:
Case 1: until the washer reaches its top spin
Initial angular speed ωi = 0 rev /s
Final angular speed ωf = 7 rev /s
Time t = 9 s
The angular acceleration is
ωf - ωi = α t
α = 7 - 0 / 9
[tex]= 0.77rev/s^2[/tex]
The angular displacement
[tex]θ_1 = \omega_i t + (1/2) \alpha t^2[/tex]
[tex]=0 + (1/2)(0.77)(9)^2[/tex]
= 31.185 rev
Case II: the washer coming to rest from top spin
Initial angular speed ωi = 7 rev /s
Final angular speed ωf = 0 rev /s
Time t = 11 s
The angular acceleration is
ωf - ωi = α t
α = 0 - 7 / 11
= - 0.63 rev/s^2
The angular displacement
[tex]\theta_2 = \omega_i t + (1/2)\alpha t^2[/tex]
[tex]=7(11) + (1/2) (-0.63)(11)^2[/tex]
=38.885 rev
Total number of revolutions
θ1 + θ2 = 31.185 rev + 38.885 rev
= 69.970 rev
