/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 5 A father racing his son has half... [FREE SOLUTION] | 91Ó°ÊÓ

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A father racing his son has half the kinetic energy of the son, who has half the mass of the father. The father speeds up by \(1.0 \mathrm{~m} / \mathrm{s}\) and then has the same kinetic energy as the son. What are the original speeds of (a) the father and (b) the son?

Short Answer

Expert verified
Father's original speed: 1 m/s; Son's original speed: 2 m/s.

Step by step solution

01

Identify Known Variables

Let's denote the father's mass as \(m_f\) and the son's mass as \(m_s\). We know that \(m_f = 2m_s\) because the son has half the mass of the father. The initial velocities are \(v_f\) for the father and \(v_s\) for the son. The kinetic energy of the father is half that of the son initially.
02

Write the Energy Equations

The kinetic energy of the son can be expressed as \(E_s = \frac{1}{2}m_sv_s^2\) and for the father, it is \(E_f = \frac{1}{2} \times \frac{1}{2}m_s v_s^2 = \frac{1}{4}m_s v_s^2\) because it's half of the son's kinetic energy.
03

Use the Condition of Equal Kinetic Energies

When the father speeds up by 1.0 m/s, his speed becomes \(v_f + 1\). His new kinetic energy becomes \(E_f' = \frac{1}{2}m_f (v_f + 1)^2\). Since this matches the son's kinetic energy, \(E_f' = E_s\).
04

Set Up the Equality

Using \(m_f = 2m_s\), substitute into the equation from Step 3 to get:\[\frac{1}{2}(2m_s)(v_f+1)^2 = \frac{1}{2}m_sv_s^2\]Simplify it to:\[(v_f+1)^2 = v_s^2\]
05

Solve for Father's and Son's Speeds

From Step 4, solve \((v_f+1)^2 = v_s^2\). Rearrange to \(v_f + 1 = v_s\) or \(v_f + 1 = -v_s\). However, speeds are positive, so \(v_f + 1 = v_s\).Substitute \(v_s = 2v_f\) from \(E_s = 2E_f\): \[ v_f + 1 = 2v_f \]Solve for \(v_f\): \[ v_f = 1 ext{ m/s} \]Substitute \(v_f\) into \(v_s = 2v_f\) to find \(v_s = 2 ext{ m/s}\).
06

Conclusion

The original speeds are \(v_f = 1 \text{ m/s}\) for the father and \(v_s = 2 \text{ m/s}\) for the son.

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Key Concepts

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

Mass and Velocity
Understanding the relationship between mass and velocity is crucial when studying kinetic energy. Kinetic energy depends on both the mass of an object and its velocity. In physics, having these two values clearly defined is essential for accurate calculations.
In this exercise, we are working with a father and son. The son has half the mass of his father, meaning if the father's mass is represented as \(m_f\), the son's mass is \(m_s = \frac{1}{2}m_f\). This setup directly affects their kinetic energies.
Velocity, on the other hand, is how fast an object is moving and in which direction. It's a vector quantity and plays a significant role in determining kinetic energy through the equation, \(KE = \frac{1}{2}mv^2\). By understanding their velocities, we can solve how kinetic energy is distributed initially and after changes in speed.
Energy Equations
Energy equations are central to solving physics problems involving motion. When we talk about kinetic energy, the formula used is \(KE = \frac{1}{2}mv^2\). This tells us how energy is related to an object's mass \((m)\) and its velocity \((v)\).
In our specific problem, initial equations are set to compare the father's and son's kinetic energies: the father's kinetic energy \(E_f\) is half of the son's \(E_s\). We express these energies mathematically as \(E_s = \frac{1}{2}m_sv_s^2\) for the son and \(E_f = \frac{1}{4}m_sv_s^2\) for the father.
When the father speeds up by 1 m/s, his new velocity changes his kinetic energy, setting up an important equality: his adjusted kinetic energy becomes equal to that of the son. This further allows us to solve the system and find specific velocity values.
Problem Solving in Physics
Problem solving in physics often requires breaking down complex scenarios into manageable pieces. First, identify and understand the known variables and conditions, as seen in our problem setup.
Then, using physics principles such as the conservation of energy or equality of forces helps in setting up relevant equations. In this example, understanding kinetic energy and how it translates into equations was vital.
After setting up your equations, it's time for logical solving and algebraic manipulation. By equating the kinetic energies and expressing all variables in terms of one another, we simplify the problem to achievable calculations. This process, while involving variables like mass and velocity, demonstrates how structured problem-solving leads to finding correct solutions of \(v_f = 1 \text{ m/s}\) and \(v_s = 2 \text{ m/s}\) for the father and son, respectively.
Finally, always verify that your solutions make physical sense within the context given.

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Most popular questions from this chapter

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