9. The disc in the hard drive of a computer rotates at 7200...

9. The disc in the hard drive of a computer rotates at 7200 rpm. (a) What is the disc's angular velocity in radians per second? (b) If the reading head of the drive is located 3.00 cm from the rotation axis, what is the linear speed of a point on the disc just below it?

Transcript

0:00 Hi there.

00:01 So for this problem, we are told that the platter of the hard drive of a computer rotates with 7 ,200 revolutions per minute.

00:21 And so for part a of this problem, we are asked about what is the angular velocity in radiance per second of the point? platter.

00:36 So to solve this part of the problem, we use dimensional analysis.

00:42 So we have 7 ,200 revolutions per minute.

00:51 So we know that there are two times pi radiance in one revolution.

01:00 And we also know that there is one minute and 60 seconds.

01:09 So with this information we can pass from revolutions per minute to radiance per seconds because we can cancel this one with this one and this one with this one.

01:21 So we obtain a value of 753 .98 radiance per second.

01:30 So that's a solution for part a of this problem.

01:36 Now for part b, we are told that if the reading head of the drive is located 3 centimeters from the rotational axis, what is the linear speed off the point on the platter just below it? so, in this case we are given the value of the radius that is 3 centimeters in meters.

02:06 This is 0 .03 meters.

02:11 And then we can obtain the linear speed by just making the product between the radius and the angular speed.

02:22 So we just substitute the value that we just have obtained from part a of this problem and the radius that we have in here...

Question

9. The disc in the hard drive of a computer rotates at 7200 rpm. (a) What is the disc's angular velocity in radians per second? (b) If the reading head of the drive is located 3.00 cm from the rotation axis, what is the linear speed of a point on the disc just below it?

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