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\(A 45.0 \mathrm{~kg}\) woman stands up in a \(60.0 \mathrm{~kg}\) canoe \(5.00 \mathrm{~m}\) long. She walks from a point \(1.00 \mathrm{~m}\) from one end to a point \(1.00 \mathrm{~m}\) from the other end (Fig. \(\mathrm{P} 8.92\) ). If you ignore resistance to motion of the canoe in the water, how far does the canoe move during this process?

Short Answer

Expert verified
Once you have solved the equation derived in Step 4, you get the canoe's movement. Make sure you interpret the direction (negative or positive) correctly. Also, note that while the canoe moves in water, this motion is relative to the ground, not the water itself.

Step by step solution

01

Understand the Principle of Conservation of Center of Mass

Remember, for any system free from external forces, the center of mass stays constant or conserves. Here the total system is woman + canoe and the external forces (earth's gravity and buoyancy from the water) cancel each other out, so the total center of mass will not move.
02

Calculate the Initial Position of the Center of Mass

First, let's calculate the initial center of mass of the system before the woman moves. Assuming one end of the canoe as reference point (the origin) and positive direction is towards the other end, the position of center of mass (\(x_{cm}\)) is given by: \[x_{cm1} = \frac{(m_{woman}\cdot x_{woman1}) + (m_{canoe}\cdot x_{canoe1})}{(m_{woman} + m_{canoe})}\] where \(m_{woman} = 45.0 \mathrm{~kg}\) is the woman mass, \(x_{woman1} = 1.00 \mathrm{~m}\) is the woman's initial position, \(m_{canoe} = 60.0 \mathrm{~kg}\) is the canoe mass, and \(x_{canoe1} = 2.50 \mathrm{~m}\) is the canoe's initial center (as it's at the center of the canoe).
03

Calculate the Final Position of the Center of Mass

After the woman moves, the center of the system changes. The final center of mass (\(x_{cm2}\)) is given by: \[x_{cm2} = \frac{(m_{woman}\cdot x_{woman2}) + (m_{canoe}\cdot x_{canoe2})}{(m_{woman} + m_{canoe})}\] with \(x_{woman2} = 4.00 \mathrm{~m}\), the woman's final position. However, we are actually interested in the final center of mass of the canoe, so let's assume \(x_{canoe2}\) is unknown and \(x_{cm2}\) should be equal to \(x_{cm1}\) due to conservation of the center of mass.
04

Calculate the Canoe's Movement

Now, from step 3, we know that \(x_{cm1} = x_{cm2}\), so we have the following equation: \[(m_{woman}\cdot x_{woman1}) + (m_{canoe}\cdot x_{canoe1}) = (m_{woman}\cdot x_{woman2}) + (m_{canoe}\cdot x_{canoe2})\] Solve this equation for \(x_{canoe2}\), and by subtracting \(x_{canoe1}\) from \(x_{canoe2}\), we shall get how far the canoe moved.

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Key Concepts

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

Physics Problem Solving
When faced with a physics problem, a clear and systematic approach is essential for successfully arriving at a solution. Let's consider a situation where a person maneuvers within a floating canoe. This exercise exemplifies how physics problem solving often involves breaking down a complex scenario into manageable parts.

Initially, we identify the relevant principles that apply to the situation—in this case, the principle of conservation of center of mass. Next, we define the system, which includes all objects whose motion we are interested in understanding. Here, the system comprises the woman and the canoe. After establishing the system and principles, we proceed to quantify the initial and final states. We calculate the center of mass for both states, ensuring that it adheres to the conservation principle. It's important to remain meticulous with units and careful with calculations.

The essence of physics problem solving lies in the methodical application of concepts to find quantitative results, which can often be achieved through a step-by-step process, just as illustrated in solving this canoe conundrum.
System Momentum Conservation
In mechanics, the conservation of momentum is a fundamental concept, particularly when dealing with isolated systems—an object or group of objects that do not interact with external forces. This principle is at the core of understanding the canoe problem.

Since there are no external forces acting horizontally on the woman-canoe system (ignoring the resistance of the canoe in the water), the system's momentum must be conserved. This leads us to the conclusion that any motion of the woman within the canoe must be accompanied by a reaction that maintains the overall momentum of the system at zero. Essentially, as the woman walks, the canoe moves in the opposite direction to ensure the center of mass of the system remains unchanged. This is a perfect illustration of Newton's third law, which states that for every action, there is an equal and opposite reaction.

It is the delicate dance between the woman's weight and movement and the canoe's corresponding reaction that highlights system momentum conservation. This principle allows us to calculate how far the canoe moves to compensate for the woman's shift in position.
Mechanics in Physics
Mechanics is the branch of physics concerned with the behavior of physical bodies when subjected to forces or displacements. Central to mechanics are the concepts of motion, forces, mass, and energy. The canoe scenario is an application of classical mechanics, where we study the motions of objects under the influence of a balance of forces.

In the absence of an external force, the canoe problem showcases how the center of mass for a system remains stationary even though individual elements within that system may be in motion. This is a key principle in mechanics called the conservation of the center of mass. By understanding this and other mechanical principles, such as Newton's laws of motion, one can analyze and predict the movement of objects in a variety of complex situations.

Throughout the resolution of the canoe challenge, concepts such as mass, force, equilibrium, and displacement come into play, reflecting the pervasive nature of mechanics in describing the physical world around us. The ability to reason through such problems is a coveted skill within the realm of physics, and it's through exercises like these that students gain a deeper grasp of mechanics in action.

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Most popular questions from this chapter

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