Acomputer hard disk 8.0 cm in diameter is initially at rest. a small dot is painted on the edge of the disk. the disk accelerates at 610 rad/s2 for 12s, then coasts at a steady angular velocity for another 12s.
a. what is the speed of the dot at t = 1.0 s? 12m/s
b. through how many revolutions has it turned?

a) 282.8 m/s

b) 13812 revolutions

Explanation:

a) The aceleration(a) is the angular velocity(w) divide by the time. The disk had cosated for 12 s in a constant angular velocity, so it will be:

a = w/t

610 = w/12

w = 7230 rad/s

The angular velocity is related by the linear velocity:

V = w*r, where r is the radius of the circumference ( r = 0.08/2 = 0.04 m)

V = 7230*0.04 = 292.8 m/s

b) The number of revolutions is the frequency (f) of the moviment, which is related to the angular velocity as:

w = 2π*f

f = w/2π

f = 7230/6.28

f = 1151 revolutions/s

So, the total revolutions (n) is 12 s was:

n = 12*1151 = 13812 revolutions

i think it’s a. this is because if they measured the mass of something with a mass of 150g, then their final answer would have to be approximately 150g. though all of their answers are almost 150, rosa and tran have the closest answers (or the exact answer) to the accurate one.