Equations of Rotational Motion Video Lessons

Concept

# Problem: A computer disk drive is turned on starting from rest and has a constant angular acceleration. If it took 0.0865 s for the drive to make its second revolution, (a) how long did it take to make the first complete revolution, and (b) what is its angular acceleration, in rad/s2?

###### FREE Expert Solution

Rotational kinematic equations:

For the first round:

• t1 = t s
• θ1 = 2π
• α1 = α (constant)
• ω1 = ?

For the second round:

• t2 = (t + 0.0865) s
• α2 = α (constant)
• ω2 = ?

(a)

We need an expression that does not have ω (ω1, ω2):

θ1 = ω0t1 + (1/2)αt12

2π = 0 + (1/2)(α)(t2)  Equation 1

θ2 = ω0t2 + (1/2)αt22

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###### Problem Details

A computer disk drive is turned on starting from rest and has a constant angular acceleration. If it took 0.0865 s for the drive to make its second revolution,

(a) how long did it take to make the first complete revolution, and

(b) what is its angular acceleration, in rad/s2?