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A \(1.50 \mathrm{~kg}\) mass on a spring has displacement as a function of time given by $$ x(t)=(7.40 \mathrm{~cm}) \cos [(4.16 \mathrm{rad} / \mathrm{s}) t-2.42] $$ Find (a) the time for one complete vibration; (b) the force constant of the spring; (c) the maximum speed of the mass; (d) the maximum force on the mass; (e) the position, speed, and acceleration of the mass at \(t=1.00 \mathrm{~s} ;\) (f) the force on the mass at that time.

Short Answer

Expert verified
The time for one complete vibration is \(1.51s\), the force constant of the spring is \(131N/m\), the maximum speed of the mass is \(0.308m/s\), the maximum force on the mass is \(9.68N\), and at t=1s, its position, speed, and acceleration are \(0.043m\), \(0.066m/s\), and \(-1.16m/s^2\) respectively, and the force on the mass at that time is \(5.65N\).

Step by step solution

01

Determining the time for a complete vibration

The time of one complete vibration, also known as the period T, can be calculated from angular frequency \(\omega\) in the harmonic oscillator model. The angular frequency is given by \(\omega = \frac{2\pi}{T}\). So, T = \(\frac{2\pi}{\omega}\). From the equation, we can see that the angular frequency \(\omega = 4.16 \, rad/s\). Substitute this into the formula to find T.
02

Calculating the force constant of the spring

The force constant k of the spring can be obtained from the formula \(\omega = \sqrt{\frac{k}{m}}\), where m is the mass of the object. Rearranging for k we get, k = \(m \times \omega^2\). The mass m=1.5kg and \(\omega\) is as calculated before, substitute these values in to find k.
03

Determining the maximum speed of the mass

The maximum speed vmax of the mass occurs when the spring is at its equilibrium position and can be calculated by multiplying the amplitude A and the angular frequency \(\omega\). Vmax = \(A \times \omega\). From the equation, the amplitude A=7.4cm or 0.074m. So, substitute the values in to find the maximum speed.
04

Finding the maximum force on the mass

The maximum force Fmax occurs at maximum extension or contraction and is calculated by multiplying the force constant k and the amplitude A. Fmax = \(k \times A\). Substitute the values of k and A in to find the maximum force.
05

Calculation of position, speed, acceleration at t=1s

At t=1s, the position x, speed v, and acceleration a can be calculated using the formulas for harmonic oscillators. Position x is given by the displacement function itself. Speed v and acceleration a can be calculated by taking first and second derivatives of the displacement function respectively.
06

Calculating the force on mass at t=1s

The force F on the mass at any instant can be calculated using Hooke’s law, which is the product of the force constant k and displacement at that instant. Substitute the value of k and the calculated position at 1s to find the force at t=1s.

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Key Concepts

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

Angular Frequency
Angular frequency is a fundamental concept when dealing with harmonic oscillators, such as masses on springs. It is denoted by the Greek letter omega (\( \omega \)) and shows how fast the mass moves through its cycle. The angular frequency is related to the period (\( T \)) of oscillation, which is the time for one cycle, by the formula \( \omega = \frac{2\pi}{T} \). This means that if the angular frequency is high, the mass goes through more cycles in a given time period, making it oscillate faster.

The given problem provides the angular frequency of \( 4.16 \, \text{rad/s} \). This means that the mass completes \( 4.16 \) radians per second. To find the period, you rearrange the formula to \( T = \frac{2\pi}{\omega} \). Simply substitute the value of\( \omega \) to get \( T \).

Understanding how angular frequency works helps us determine how fast an object will oscillate in systems like pendulums or springs. It serves as a key determinant of the system's state of motion.
Spring Force Constant
The spring force constant, also known as Hooke's constant, is a crucial factor in understanding how stiff a spring is. It is denoted by the symbol \( k \) and measures how much force is needed to extend or compress the spring by a unit length. This principle is given by Hooke's Law, which we'll discuss later.

In our problem, the spring constant can be calculated using the relationship \( \omega = \sqrt{\frac{k}{m}} \), where \( m \) is the mass attached to the spring. Rearranging gives \( k = m \times \omega^2 \). Simply plug in the values for \( m = 1.5 \, \text{kg} \) and \( \omega = 4.16 \, \text{rad/s} \), then solve for \( k \).

A larger value of \( k \) signifies a stiffer spring that requires more force for the same extension compared to a spring with a smaller \( k \). It is fundamental in defining the characteristics of the spring's behavior.
Maximum Speed
The maximum speed of an object oscillating in harmonic motion, like a spring-mass system, is another key parameter. It indicates the highest speed the mass reaches during its oscillation cycle. The maximum speed occurs when the object passes through the equilibrium position, where the spring force and displacement are zero.

To calculate the maximum speed in a harmonic oscillator, use the formula: \( V_{\text{max}} = A \times \omega \), where \( A \) is the amplitude, and \( \omega \) is the angular frequency. From the given data, \( A = 7.4 \, \text{cm} = 0.074 \, \text{m} \) and \( \omega = 4.16 \, \text{rad/s} \). By substituting these values into the formula, you can find the maximum speed of the mass.

Understanding maximum speed can help predict the performance and stability of mechanical systems that involve periodic motion, from amusement park rides to industrial machinery.
Hooke's Law
Hooke's Law is a principle that defines the behavior of springs and their force response to deformation. It is expressed as \( F = -kx \), where \( F \) is the restoring force exerted by the spring, \( k \) is the spring constant, and \( x \) is the displacement from the equilibrium position. The negative sign indicates that the force exerted by the spring is always opposite to the direction of displacement, pulling back towards the equilibrium position.

In the scenario where a mass is attached to a spring, Hooke's Law can be used at any instant to calculate the force the spring exerts on the mass. At maximum displacement, the force is greatest. You can also use Hooke's Law to find the force at a specific instant, such as at \( t = 1 \text{ s} \), by substituting the calculated displacement of the mass into the formula.

This law is fundamental in physics and engineering because it describes how elastic materials respond to mechanical stress. It helps in designing a wide variety of devices and structures where spring dynamics play a role.

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Most popular questions from this chapter

An object is undergoing SHM with period \(0.300 \mathrm{~s}\) and amplitude \(6.00 \mathrm{~cm} .\) At \(t=0\) the object is instantaneously at rest at \(x=6.00 \mathrm{~cm}\). Calculate the time it takes the object to go from \(x=6.00 \mathrm{~cm}\) to \(x=-1.50 \mathrm{~cm}\)

You want to find the moment of inertia of a complicated machine part about an axis through its center of mass. You suspend it from a wire along this axis. The wire has a torsion constant of \(0.450 \mathrm{~N} \cdot \mathrm{m} / \mathrm{rad}\). You twist the part a small amount about this axis and let it go, timing 165 oscillations in \(265 \mathrm{~s}\). What is its moment of inertia?

A slender rod of length \(80.0 \mathrm{~cm}\) and mass \(0.400 \mathrm{~kg}\) has its center of gravity at its geometrical center. But its density is not uniform; it increases by the same amount from the center of the rod out to either end. You want to determine the moment of inertia \(I_{\mathrm{cm}}\) of the rod for an axis perpendicular to the rod at its center, but you don't know its density as a function of distance along the rod, so you can't use an integration method to calculate \(I_{\mathrm{cm}}\). Therefore, you make the following measurements: You suspend the rod about an axis that is a distance \(d\) (measured in meters) above the center of the rod and measure the period \(T\) (measured in seconds) for small-amplitude oscillations about the axis. You repeat this for several values of \(d\). When you plot your data as \(T^{2}-4 \pi^{2} d / g\) versus \(1 / d\), the data lie close to a straight line that has slope \(0.320 \mathrm{~m} \cdot \mathrm{s}^{2} .\) What is the value of \(I_{\mathrm{cm}}\) for the rod?

A \(2.00 \mathrm{~kg},\) frictionless block is attached to an ideal spring with force constant \(300 \mathrm{~N} / \mathrm{m}\). At \(t=0\) the spring is neither stretched nor compressed and the block is moving in the negative direction at \(12.0 \mathrm{~m} / \mathrm{s} .\) Find (a) the amplitude and (b) the phase angle. (c) Write an equation for the position as a function of time.

A machine part is undergoing SHM with a frequency of \(4.00 \mathrm{~Hz}\) and amplitude \(1.80 \mathrm{~cm} .\) How long does it take the part to go from \(x=0\) to \(x=-1.80 \mathrm{~cm} ?\)

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