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BIO Weighing Astronauts. This procedure has actually been used to "weigh"" astronauts in space. A 42.5 -kg chair is attached to a spring and allowed to oscillate. When it is empty, the chair takes 1.30 s to make one complete vibration. But with an astronaut sitting in it, with her feet off the floor, the chair takes 2.54 s for one cycle. What is the mass of the astronaut?

Short Answer

Expert verified
The mass of the astronaut is approximately 81.34 kg.

Step by step solution

01

Understand the Problem

We need to find the mass of the astronaut. The chair and astronaut together create a harmonic oscillator, where the empty chair and the chair with the astronaut have different oscillation periods.
02

Formula for Period of Spring

The period of oscillation for a spring-mass system is given by the formula \( T = 2\pi\sqrt{\frac{m}{k}} \), where \( T \) is the period, \( m \) is the mass, and \( k \) is the spring constant.
03

Find Spring Constant

First, we calculate the spring constant \( k \) using the period of the empty chair. For the chair alone with a mass of 42.5 kg and period 1.30 s, we rearrange the formula to find \( k \):\[ k = \frac{4\pi^2\times m_{chair}}{T_{chair}^2} = \frac{4\pi^2\times 42.5}{1.30^2} \]
04

Calculate Empty Chair Spring Constant

Calculate the spring constant using the values:\[ k = \frac{4\pi^2\times 42.5}{1.30^2} \approx 985.96 \text{ N/m} \]
05

Calculate Total Mass with Astronaut

Now use the period with the astronaut to find the total mass \( m + m_{astronaut} \):\[ T_{total} = 2.54 = 2\pi\sqrt{\frac{m_{total}}{985.96}} \]Solve for \( m_{total} \):\[ m_{total} = \frac{T_{total}^2\times k}{4\pi^2} \approx \frac{2.54^2 \times 985.96}{4\pi^2} \approx 123.84 \text{ kg} \]
06

Calculate Astronaut's Mass

Now subtract the mass of the chair from the total mass to find the astronaut's mass:\[ m_{astronaut} = m_{total} - m_{chair} = 123.84 - 42.5 = 81.34 \text{ kg} \]

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Key Concepts

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

Oscillation Period
The oscillation period is an essential concept in understanding how spring-mass systems function. It is the time taken for one complete cycle of oscillation. In a harmonic oscillator like a spring-mass system, the period depends on both the mass attached to the spring and the spring's stiffness, known as the spring constant. Using the simple formula, \( T = 2\pi\sqrt{\frac{m}{k}} \), where \( T \) is the period, \( m \) is the mass, and \( k \) is the spring constant, we can see how the mass and spring constant influence the duration of one cycle.

When an object, such as a chair or an astronaut seated on it, is set into motion on a spring, it follows a periodic path. The empty chair's oscillation period of 1.30 seconds indicates how quickly it can go through one full vibration. On adding mass, like an astronaut, the period increases to 2.54 seconds, due to the increased mass slowing down the motion of the system.
Spring Constant
The spring constant, \( k \), is a measure of a spring's stiffness. It tells us how much force is needed to stretch or compress the spring by a specific distance. The spring constant is a crucial part of determining the behavior of spring-mass systems, as indicated in Hooke's Law: \( F = kx \), where \( F \) is the force applied and \( x \) is the displacement of the spring from its resting position.

To find the spring constant in the problem, we initially use the oscillation period of the empty chair. By rearranging the formula \( T = 2\pi\sqrt{\frac{m}{k}} \), and solving for \( k \), we obtain:- \( k = \frac{4\pi^2 \times m_{chair}}{T_{chair}^2} \).
This calculation reveals that the spring constant is approximately 985.96 N/m, illustrating the relative stiffness of the spring used.
Harmonic Motion
Harmonic motion refers to the repetitive, oscillating movement in a system, like a spring-mass setup. The chair and the astronaut combination is an example of such a system. This motion is characterized by its periodic nature - meaning it repeats in a predictable and regular fashion.

In a harmonic oscillator, like a spring, the dynamics are determined largely by the mass and the spring constant. As the mass of the system increases (such as when the astronaut sits on the chair), the motion's period lengthens. This is because heavier objects require more force to return to their rest position, thus slowing down the cycle.

Understanding these dynamics helps predict how other similar systems might behave under varying masses, which is critical for applications ranging from engineering to understanding astronaut dynamics in space.
Mass Calculation in Microgravity
In a microgravity environment, such as space, traditional scales do not function correctly. Instead, systems like the spring-mass harmonic oscillator described in this scenario are used to "weigh" or determine mass. The method relies on the principles of harmonic motion where the oscillation period is directly related to the mass of the object.

To find the astronaut's mass, the oscillation period when seated in the chair is used, along with the calculated spring constant. Subtracting the known mass of the chair from the total calculated mass of the system (when the astronaut is seated), gives the astronaut's mass: - Total mass = 123.84 kg - Chair's mass = 42.5 kg - Astronaut's mass = Total mass - Chair's mass = 81.34 kg

This method not only demonstrates an elegant solution to finding mass without gravity but also highlights the ingenuity required in adapting to space environments.

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Most popular questions from this chapter

A uniform, solid metal disk of mass 6.50 \(\mathrm{kg}\) and diameter 24.0 \(\mathrm{cm}\) hangs in a horizontal plane, supported at its center by a vertical metal wire. You find that it requires a horizontal force of 4.23 \(\mathrm{N}\) tangent to the rim of the disk to turn it by \(3.34^{\circ},\) thus twisting the wire. You now remove this force and release the disk from rest. (a) What is the torsion constant for the metal wire? (b) What are the frequency and period of the torsional oscillations of the disk? (c) Write the equation of motion for the disk.

When a body of unknown mass is attached to an idealspring with force constant \(120 \mathrm{N} / \mathrm{m},\) it is found to vibrate with a frequency of 6.00 \(\mathrm{Hz}\) . Find (a) the period of the motion; (b) the angular frequency; (c) the mass of the body.

\(\mathrm{A} 0.500\) -kg mass on a spring has velocity as a function of time given by \(v_{x}(t)=-(3.60 \mathrm{cm} / \mathrm{s}) \sin \left[\left(4.71 \mathrm{s}^{-1}\right) t-\pi / 2\right]\) What are (a) the period; (b) the amplitude; (c) the maximum acceleration of the mass; (d) the force constant of the spring?

Four passengers with combined mass 250 kg compress the springs of a car with worn-out shock absorbers by 4.00 \(\mathrm{cm}\) when they get in. Model the car and passengers as a single body on a single ideal spring. If the loaded car has a period of vibration of 1.92 s, what is the period of vibration of the empty car?

After landing on an unfamiliar planet, a space explorer constructs a simple pendulum of length 50.0 \(\mathrm{cm} .\) She finds that the pendulum makes 100 complete swings in 136 s. What is the value of \(g\) on this planet?

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