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Two identical \(1.50 \mathrm{~kg}\) masses are pressed against opposite ends of a light spring of force constant \(1.75 \mathrm{~N} / \mathrm{cm}\), compressing the spring by \(20.0 \mathrm{~cm}\) from its normal length. Find the speed of each mass when it has moved free of the spring on a frictionless, horizontal lab table.

Short Answer

Expert verified
Each mass moves at approximately 1.53 m/s.

Step by step solution

01

Identify the Relevant Concepts

In this exercise, we use the conservation of energy principle. Initially, the system's energy is stored as potential energy in the compressed spring. As the spring returns to its normal length, this potential energy gets converted into kinetic energy of the masses.
02

Calculate Initial Potential Energy in the Spring

The potential energy stored in a compressed or stretched spring is given by the formula \( U = \frac{1}{2} k x^2 \), where \( k \) is the spring constant and \( x \) is the compression distance.Given: \( k = 1.75 \, \text{N/cm} = 175 \, \text{N/m} \) and \( x = 20.0 \, \text{cm} = 0.20 \, \text{m} \).Hence, \( U = \frac{1}{2} \times 175 \, \text{N/m} \times (0.20 \, \text{m})^2 = 3.50 \, \text{J} \).
03

Apply Conservation of Energy

When the spring is fully decompressed, all the potential energy is converted to kinetic energy of the masses.For two masses, the total kinetic energy \( K \) is given by \( K = 2 \times \frac{1}{2} m v^2 = m v^2 \). Here, \( m = 1.50 \, \text{kg} \) is the mass of one object.
04

Solve for Speed of Each Mass

Using the energy conservation equation, \( 3.50 \, \text{J} = 1.50 \, \text{kg} \times v^2 \).Solving for \( v \), we get:\[ v^2 = \frac{3.50 \, \text{J}}{1.50 \, \text{kg}} \approx 2.33 \, \text{m}^2/\text{s}^2 \]Thus, \[ v = \sqrt{2.33 \, \text{m}^2/\text{s}^2} \approx 1.53 \, \text{m/s} \].
05

Verify the Results

Check the units and calculation to ensure no errors were made. Given that all initial potential energy is converted to kinetic energy, the calculated speed seems reasonable for typical mechanical energy conversion in such a setup.

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Key Concepts

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

Potential Energy
Potential energy is stored energy that depends on the position or configuration of an object. In our exercise, the potential energy is stored in a spring when it is compressed from its normal length. This type of potential energy is called elastic potential energy. The amount of energy stored is determined by how much the spring is compressed or stretched and is calculated using the formula:\[ U = \frac{1}{2} k x^2 \]where:
  • \( U \) is the potential energy
  • \( k \) is the spring constant, which is a measure of the spring's stiffness
  • \( x \) is the amount of compression or stretch from the spring's original length
The potential energy is the maximum when the spring is either fully compressed or fully extended.
Kinetic Energy
Kinetic energy is the energy of motion. Whenever an object is moving, it possesses kinetic energy. In the exercise scenario, as the spring decompresses, the stored potential energy turns into kinetic energy, causing the masses to move. The formula to calculate kinetic energy is:\[ K = \frac{1}{2} mv^2 \]where:
  • \( K \) is the kinetic energy
  • \( m \) is the mass of the moving object
  • \( v \) is the speed or velocity of the object
Kinetic energy is influenced by both the mass of the object and its speed, meaning heavier and faster objects have more kinetic energy. As observed in the exercise, the initial potential energy stored in the spring transforms into the kinetic energy of the masses.
Spring Constant
The spring constant, denoted by \( k \), is a fundamental concept when dealing with springs and potential energy. It defines how stiff a spring is: the larger the spring constant, the stiffer the spring. Our exercise involves a spring with a spring constant of \( 1.75 \, \text{N/cm} \), or converted into standard SI units, \( 175 \, \text{N/m} \). The spring constant is essential in calculating the potential energy stored in the spring.Factors impacting the spring constant include the material the spring is made from and its coil dimensions. A high spring constant means a more robust spring, requiring more force to compress or extend it. In our context, knowing the spring constant allows us to determine the potential energy stored when the spring is compressed.
Energy Conversion
Energy conversion refers to the transition of energy from one form to another. In mechanical systems, such as springs, energy conversion is a pivotal process. In our exercise, the stored potential energy in the spring changes into kinetic energy. This illustrates the principle of conservation of energy, where energy cannot be created or destroyed; it only changes forms. Here’s how the conversion unfolds in our scenario:
  • The spring, when compressed, holds potential energy.
  • As the spring decompresses, this potential energy starts to convert into the kinetic energy of the masses.
  • Eventually, all potential energy is transformed into kinetic energy, as evidenced by the masses starting their motion with the calculated speed.
Understanding this conversion is crucial, as it helps explain how energy behaves within mechanical systems and forms the basis of many real-world physics applications.

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Most popular questions from this chapter

A \(0.4 \mathrm{~kg}\) stone is thrown horizontally at a speed of \(20 \mathrm{~m} / \mathrm{s}\) from a \(40-\mathrm{m}\) -tall building. (a) Determine the \(x\) and \(y\) components of the stone's momentum the moment after it is thrown. (b) What are the components of its momentum just before it hits the ground? What impulse did gravity impart to the stone?

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