# Another Circular motion question

• laker_gurl3
In summary, the outside edge of the record moves 2.34 times as fast when the frequency is raised to 78 rpm.
laker_gurl3
thanks so much for any help..work and formula used would be appreciated...

A record of diameter 30cm roates on a turntable at 33.3r/min.

a.) How fast is the outside edge of the record moving?

b.) how many times as fast would it move if the frequency were raised to 78 r/min.?

laker_gurl3 said:
thanks so much for any help..work and formula used would be appreciated...

A record of diameter 30cm roates on a turntable at 33.3r/min.

a.) How fast is the outside edge of the record moving?

b.) how many times as fast would it move if the frequency were raised to 78 r/min.?

a) if the whole record moves at 33.3 revs per min, then a point on the outside edge does as well, which means that point has to go around the circumfrence (C) of the record within the minute, your speed= C/min.

b) same idea as part a, change the frequecny, and then compare.

so i did this out..for A.) i got 3138m/s
for B.) i got 7351m/s, therefore it's 2.34 times as fast...is that correct?

ok ya, i mean it had to go around the circumfrence 33.3 times per minute, but that's what you did, so good. Those are the numbers i got, except your units are wrong, its cm/min not m/s.

Gale,i get double for the first number...

$$v=\omega R \ [m \ s^{-1}]$$

R=0.3m

$$\omega=2\pi \nu=\left(2\pi \ \mbox{rad}\right) \left(\frac{33.3}{60} \ Hz \right) \simeq \frac{200\pi}{180} \mbox{rad} \ s^{-1}$$

Ergo

$$v\simeq \frac{\pi}{3} m \ s^{-1} = \frac{6000\pi}{3} cm \ (min)^{-1}$$

which is double that the # you referred to in post #4.

Daniel.

EDIT:As Gale pointed out,the radius is only 0.15m.So that explains the incorrect result i got.

Last edited:
you got double because you let R=.3 whereas .3 is the diameter.

****.

Daniel.

## 1. What is circular motion?

Circular motion is a type of motion in which an object moves in a circular path around a central point.

## 2. What causes circular motion?

Circular motion is caused by a force acting towards the center of the circle, known as centripetal force. This force is necessary to keep the object moving in a circular path.

## 3. How is circular motion related to velocity and acceleration?

In circular motion, the velocity of the object is constantly changing as it moves around the circle, even if the speed remains constant. This change in velocity results in acceleration, which is always directed towards the center of the circle.

## 4. What is the difference between uniform and non-uniform circular motion?

Uniform circular motion is when an object moves at a constant speed around a circle, while non-uniform circular motion is when the speed of the object changes as it moves around the circle.

## 5. How is circular motion used in real life?

Circular motion is used in many real-life applications, such as the motion of planets around the sun, the motion of a Ferris wheel, and the motion of a car turning around a curve. It is also used in sports, such as the motion of a ball in a game of basketball or the motion of a runner around a track.

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