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A mass hanging from a spring is set in motion, and its ensuing velocity is given by \(v(t)=2 \pi\) cos \(\pi t\) for \(t \geq 0 .\) Assume the positive direction is upward and \(s(0)=0\). a. Determine the position function, for \(t \geq 0\) b. Graph the position function on the interval [0,4] c. At what times does the mass reach its low point the first three times? d. At what times does the mass reach its high point the first three times?

Short Answer

Expert verified
\(s(t) = 2\sin(\pi t) + C\) To determine the constant of integration C, we will use the initial condition: when t = 0, the position is 2 cm above the equilibrium (s(0) = 2). \(s(0) = 2\sin(\pi \cdot 0) + C = 2\) \(C = 2\) Therefore, the position function is: \(s(t) = 2\sin(\pi t) + 2\) for \(t ≥ 0\) #b. Graph the position function on the interval [0, 2]# Using graphing software or a graphing calculator, graph the position function \(s(t) = 2\sin(\pi t) + 2\) on the interval [0, 2]. The graph should display a sinusoidal wave with an amplitude of 2 and a period of 2. #c. Determine the times when the mass reaches its low and high points for the first three times# To find the high points, we identify the points where the derivative of the position function, which is the velocity function, changes from positive to negative. The velocity function is \(v(t) = 2\pi \cos(\pi t)\). Set it equal to zero and solve for t: \(2\pi \cos(\pi t) = 0\) \(\cos(\pi t) = 0\) Since a cosine function equals zero at odd multiples of \(\frac{\pi}{2}\), the high points occur when: \(\pi t = \frac{\pi}{2} + 2k\pi\), where \(k\) is any integer. Now, solve for the three smallest \(t\) values: 1) \(k = 0: \pi t = \frac{\pi}{2} \Rightarrow t = \frac{1}{2}\) 2) \(k = 1: \pi t = \frac{\pi}{2} + 2\pi \Rightarrow t = \frac{5}{2}\) 3) \(k = 2: \pi t = \frac{\pi}{2} + 4\pi \Rightarrow t = \frac{9}{2}\) The high points occur at \(t = \frac{1}{2}\), \(\frac{5}{2}\), and \(\frac{9}{2}\). Similarly, to find the low points, we identify points where the velocity changes from negative to positive. Since a cosine function equals zero at odd multiples of \(\pi\), the low points occur when: \(\pi t = \pi + 2k\pi\), where \(k\) is any integer. Again, solve for the three smallest t values: 1) \(k = 0: \pi t = \pi \Rightarrow t = 1\) 2) \(k = 1: \pi t = 3\pi \Rightarrow t = 3\) 3) \(k = 2: \pi t = 5\pi \Rightarrow t = 5\) The low points occur at \(t = 1\), \(3\), and \(5\). In summary, the position function for the mass hanging from the spring is \(s(t) = 2\sin(\pi t) + 2\) for \(t ≥ 0\). The high points are at \(t = \frac{1}{2}\), \(\frac{5}{2}\), and \(\frac{9}{2}\) while the low points are at \(t = 1\), \(3\), and \(5\).

Step by step solution

01

Integrate the velocity function

Begin by finding the integral of the velocity function \(v(t) = 2\pi \cos (\pi t)\). \(s(t) = \int v(t) \ dt = \int 2\pi \cos (\pi t) \ dt\). Now, integrate the function.

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Key Concepts

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

Integrating Velocity Function
The velocity function of an object describes how its velocity changes over time, providing crucial information about its motion. When we have the velocity function, integrating it gives us the position function, which tells us the location of the object at any given time.

In our exercise, the velocity function is given by \(v(t) = 2\pi\cos(\pi t)\). To find the position function, we need to integrate this velocity function with respect to time. Since the velocity changes as the cosine function oscillates, the integration will tell us the total displacement over time. Given that \(s(0) = 0\), we take the definite integral from 0 to \(t\) to find the position function \(s(t)\).

The integration process may involve trigonometric integration rules that replace the cosine function with its integral counterpart. This process is fundamental in solving problems related to motion where velocity is a time-dependent variable.
Position Function of a Spring Mass
The position function of a spring-mass system, like the one in our exercise, is a mathematical representation of the system's displacement from its equilibrium position over time. A spring-mass system typically exhibits harmonic motion, which can be described using trigonometric functions such as sine and cosine.

Integrating the velocity function found in the previous section gives us the position function. The initial condition that \(s(0) = 0\) indicates that the spring mass starts from its equilibrium position. By applying the correct initial conditions and constants derived from integration, we describe the exact motion of the mass on the spring, crucial for understanding systems in mechanics and physics, such as oscillators or pendulums.
Graphing Position Functions
Graphing position functions of an object can visually demonstrate how the object moves over time. This graphical representation is pivotal for understanding the behavior of the object during its motion. When graphing the position function of a spring-mass system, we expect a sinusoidal curve because the motion is harmonic.

With the position function calculated from integrating the velocity function, plotting it within a specific time interval allows us to observe the peaks and troughs corresponding to the extreme points in the spring’s motion. The position graph would have an amplitude that corresponds to the maximum displacement from the equilibrium, and the cycle's period would denote the time it takes for the motion to repeat itself.
Determining Extreme Points
Determining extreme points—where the object reaches the highest or lowest position—in the motion of a system like the spring-mass setup is significant for identifying the amplitude and understanding the system's behavior at specific points in time.

Extreme points on a position function graph are found where the slope of the tangent is zero, which corresponds to where the velocity function crosses the time axis, changing sign. By examining the position function's graph, or solving the corresponding equations, we can calculate the times at which these extreme points occur, which represent the moments when the spring-mass system is fully extended or compressed.

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