A centrifuge in a medical laboratory rotates at an angular speed of 3600 rpm (revolutions per minute). When switched off, it rotates 60.0 times before coming to rest. Find the constant angular acceleration of the centrifuge.

Short Answer

Expert verified
Answer: The constant angular acceleration of the centrifuge is -60π² radians/second².

Step by step solution

01

Convert initial angular speed to radians per second

We are given an initial angular speed of 3600 rpm (revolutions per minute). To convert this to radians per second, we use the conversion factors for minutes to seconds and revolutions to radians: \[ 1~minute = 60~seconds \] \[ 1~revolution = 2\pi~radians\] So, the conversion is: \[ \omega_0 = 3600\cdot\frac{2\pi~radians}{1~revolution} \cdot \frac{1~minute}{60~seconds} = 2\pi \times 60~radians/second \]
02

Convert the number of rotations to radians

We are given that the centrifuge rotates 60 times before coming to rest. To convert this into radians, we can use the conversion factor of 1 revolution = 2π radians: \[ \theta = 60\cdot\frac{2\pi~radians}{1~revolution} = 120\pi~radians\]
03

Use the angular kinematic equation to find the angular acceleration

Since the centrifuge comes to rest, we know that its final angular speed (ω) is 0 radians/second. We can use the following angular kinematic equation to find the constant angular acceleration (α): \[ \omega^2 = \omega_0^2 + 2\alpha\theta \] Rearrange the equation to solve for α: \[ \alpha = \frac{\omega^2 - \omega_0^2}{2\theta}\] Now plug in the values for ω, ω₀, and θ: \[ \alpha = \frac{(0)^2 - (2\pi \times 60)^2}{2(120\pi)} =-\frac{(2\pi \times 60)^2 }{2(120\pi)} \] \[ \alpha = - \frac{4\pi^2 \times 3600}{240\pi} = -60\pi^2 ~radians/second^2 \]
04

Present the final answer

The constant angular acceleration of the centrifuge is -60π² radians/second².

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Kinematic Equations
Kinematic equations are powerful tools in physics that describe the motion of objects. In the realm of angular motion, these equations get adapted to account for rotational motion, linking variables like angular displacement (\theta), angular velocity (\text{\(\omega\)}), and angular acceleration (\text{\(\alpha\)}). It's crucial to understand that angular kinematic equations are very similar to their linear counterparts, but they specifically deal with rotational movement around a circle.

For instance, when the textbook problem mentions that 'it rotates 60.0 times before coming to rest,' what we are really discussing is angular displacement, and an equation of motion links this displacement to initial angular velocity and angular acceleration, allowing us to solve for the unknown variable.
Angular Speed
Angular speed (often represented by the symbol \text{\(\omega\)}) is a measure of how quickly an object rotates or revolves relative to another point, expressed in terms such as revolutions per minute (rpm) or radians per second (rad/s). It can be thought of as the angular equivalent of linear speed.

In our exercise, the centrifuge has an initial angular speed of 3600 rpm. To make this information useful in physics calculations, it must first be converted to the standard unit of radians per second. This is because all kinematic equations require consistency in units to yield correct solutions.
Unit Conversion
Unit conversion is a fundamental skill in physics problem-solving because equations require inputs to be in consistent units. For angular measurements, radians are the standard unit, whereas in everyday scenarios, we often encounter revolutions or turns.

So, when we're given values like 3600 rpm for the angular speed, it's imperative to convert to radians per second as we did by using the conversion factors (\text{\(1~minute = 60~seconds\)}) and (\text{\(1~revolution = 2\pi~radians\)}). Careful conversion ensures that we achieve the accurate angular acceleration. Omitting or incorrectly converting units can lead to errors and incorrect results.
Physics Problem Solving
Solving physics problems involves a systematic approach of understanding concepts, applying appropriate formulas, and performing accurate calculations. Step-by-step reasoning helps break down complex problems into manageable parts, as we saw in the exercise involving a centrifuge's angular acceleration.

1. Interpret the problem and identify knowns and unknowns.
2. Choose a relevant physics principle or law.
3. Apply the appropriate formula or equation.
4. Perform precise unit conversions.
5. Insert known values and solve for the unknown.
6. Evaluate your solution to ensure it makes sense.

By applying this structured approach, we tackled the challenge of finding the angular acceleration of a decelerating centrifuge, showcasing how each step builds towards the final solution.

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Most popular questions from this chapter

A ceiling fan is rotating in clockwise direction (as viewed from below) but it is slowing down. What are the directions of \(\omega\) and \(\alpha ?\)

A typical Major League fastball is thrown at approximately \(88 \mathrm{mph}\) and with a spin rate of \(110 \mathrm{rpm} .\) If the distance between the pitcher's point of release and the catcher's glove is exactly \(60.5 \mathrm{ft},\) how many full turns does the ball make between release and catch? Neglect any effect of gravity or air resistance on the ball's flight.

A particular Ferris wheel takes riders in a vertical circle of radius \(9.0 \mathrm{~m}\) once every \(12.0 \mathrm{~s} .\) a) Calculate the speed of the riders, assuming it to be constant. b) Draw a free-body diagram for a rider at a time when she is at the bottom of the circle. Calculate the normal force exerted by the seat on the rider at that point in the ride. c) Perform the same analysis as in part (b) for a point at the top of the ride.

A carousel at a carnival has a diameter of \(6.00 \mathrm{~m}\). The ride starts from rest and accelerates at a constant angular acceleration to an angular speed of 0.600 rev/s in \(8.00 \mathrm{~s}\). a) What is the value of the angular acceleration? b) What are the centripetal and angular accelerations of a seat on the carousel that is \(2.75 \mathrm{~m}\) from the rotation axis? c) What is the total acceleration, magnitude and direction, \(8.00 \mathrm{~s}\) after the angular acceleration starts?

You are holding the axle of a bicycle wheel with radius \(35.0 \mathrm{~cm}\) and mass \(1.00 \mathrm{~kg}\). You get the wheel spinning at a rate of 75.0 rpm and then stop it by pressing the tire against the pavement. You notice that it takes \(1.20 \mathrm{~s}\) for the wheel to come to a complete stop. What is the angular acceleration of the wheel?

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