/*! 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 47 A machine carries a \(4.0 \mathr... [FREE SOLUTION] | 91Ó°ÊÓ

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A machine carries a \(4.0 \mathrm{~kg}\) package from an initial position of \(\vec{d}_{i}=(0.50 \mathrm{~m}) \hat{\mathrm{i}}+(0.75 \mathrm{~m}) \hat{\mathrm{j}}+(0.20 \mathrm{~m}) \hat{\mathrm{k}}\) at \(t=0\) to a final posi- tion of \(\vec{d}_{f}=(7.50 \mathrm{~m}) \hat{\mathrm{i}}+(12.0 \mathrm{~m}) \hat{\mathrm{j}}+(7.20 \mathrm{~m}) \hat{\mathrm{k}}\) at \(t=12 \mathrm{~s}\). The constant force applied by the machine on the package is \(\vec{F}=(2.00 \mathrm{~N}) \hat{\mathrm{i}}+(4.00 \mathrm{~N}) \hat{\mathrm{j}}+(6.00 \mathrm{~N}) \hat{\mathrm{k}}\). For that displacement, find (a) the work done on the package by the machine's force and (b) the average power of the machine's force on the package.

Short Answer

Expert verified
The work done is 101.00 J, and the average power is 8.42 W.

Step by step solution

01

Calculate the Displacement Vector

To find the displacement vector \( \vec{\Delta d} \), subtract the initial position \( \vec{d}_{i} \) from the final position \( \vec{d}_{f} \). The displacement vector is \( \vec{\Delta d} = \vec{d}_{f} - \vec{d}_{i} \).\[\vec{\Delta d} = ((7.50 - 0.50) \mathrm{~m}) \hat{\mathrm{i}} + ((12.0 - 0.75) \mathrm{~m}) \hat{\mathrm{j}} + ((7.20 - 0.20) \mathrm{~m}) \hat{\mathrm{k}} \]\[\vec{\Delta d} = (7.00 \mathrm{~m}) \hat{\mathrm{i}} + (11.25 \mathrm{~m}) \hat{\mathrm{j}} + (7.00 \mathrm{~m}) \hat{\mathrm{k}} \]
02

Calculate the Work Done

Work done \( W \) is given by the dot product of the force vector \( \vec{F} \) and the displacement vector \( \vec{\Delta d} \). \[ W = \vec{F} \cdot \vec{\Delta d} \]\[ W = (2.00 \mathrm{~N}) \times (7.00 \mathrm{~m}) + (4.00 \mathrm{~N}) \times (11.25 \mathrm{~m}) + (6.00 \mathrm{~N}) \times (7.00 \mathrm{~m}) \]\[ W = 14.00 \mathrm{~J} + 45.00 \mathrm{~J} + 42.00 \mathrm{~J} \]\[ W = 101.00 \mathrm{~J} \]
03

Calculate the Average Power

Average power \( P_{avg} \) is the total work done \( W \) divided by the total time \( t \) taken.\[ P_{avg} = \frac{W}{t} \]Given \( W = 101.00 \mathrm{~J} \) and \( t = 12 \mathrm{~s} \),\[ P_{avg} = \frac{101.00 \mathrm{~J}}{12 \mathrm{~s}} = 8.42 \mathrm{~W} \]

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Key Concepts

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

Vector Displacement
Vector displacement is a fundamental concept in physics that describes the change in position of an object. In our problem, we need to determine how the package moved from its starting point to its finishing point. This is done by calculating the displacement vector, which is essentially the difference between the initial and final positions.
To find vector displacement, we take the vector representing the final position and subtract the vector representing the initial position. This operation is straightforward, requiring the subtraction of corresponding components:
  • Subtract the initial x-coordinate from the final x-coordinate to find the i-component.
  • Do the same for the y- and z-components to find the j- and k-components, respectively.
The resulting vector tells us not just the distance but the overall movement direction of the package in three-dimensional space. This calculation is key in many physics problems, as it helps us understand the path an object takes over time.
Dot Product
The dot product is a crucial operation when working with vectors in physics, particularly when calculating work done by a force across a distance. Essentially, it allows us to determine how much of one vector goes in the direction of another. In our exercise, we use the dot product to calculate the work done by the machine's force on the package.
To compute the dot product, we multiply corresponding components of two vectors you want to analyze:
  • Multiply the i-components of the force and the displacement vectors.
  • Do the same for the j- and k-components.
  • Add all these products together.
The resultant scalar (a single number) from these calculations reflects the amount of energy transferred by the force along the direction of the displacement. Understanding the dot product helps explain how different vectors relate to each other in practical scenarios, such as applying a force to move an object.
Average Power Calculation
Average power is another important concept, representing the rate at which work is done or energy is transferred over a given time period. In this problem, we need to determine how quickly the machine's force did the work of moving the package.
The formula for average power is quite simple: it's the total work done divided by the time taken to do this work:
  • Identify the total amount of work completed, which we calculated using the dot product of force and displacement vectors.
  • Divide this work by how long it took to accomplish (in seconds, minutes, etc.).
This calculation tells us about the efficiency and performance of the system. A significant concept in many real-world applications, average power provides insight into how systems operate under various forces and movements.
Physics Problem Solving
Tackling physics problems involves several steps, using both math and critical thinking. Begin by understanding the problem and identifying what is asked. Each physics problem, like the one we have here, requires consistent steps to solve effectively.
Consider these general steps:
  • Highlight what information is given and what needs solving.
  • Determine relevant formulas and concepts (for example, using vector displacement and dot product for work calculations).
  • Carry out calculations systematically.
  • Double-check results to ensure accuracy.
Applying this structured approach allows us to break down complex problems. Considering units and symbols accurately throughout calculations avoids confusion. Whether in a classroom or in general science, these practices ensure you tackle physics questions with clarity and confidence.

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Most popular questions from this chapter

A cave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. The lift is performed in three stages, each requiring a vertical distance of \(10.0\) m: (a) the initially stationary spelunker is accelerated to a speed of \(5.00 \mathrm{~m} / \mathrm{s} ;(\mathrm{b})\) he is then lifted at the constant speed of \(5.00 \mathrm{~m} / \mathrm{s} ;\) (c) finally he is decelerated to zero speed. How much work is done on the \(80.0 \mathrm{~kg}\) rescuee by the force lifting him during each stage?

An iceboat is at rest on a frictionless frozen lake when a sudden wind exerts a constant force of \(200 \mathrm{~N}\), toward the east, on the boat. Due to the angle of the sail, the wind causes the boat to slide in a straight line for a distance of \(8.0 \mathrm{~m}\) in a direction \(20^{\circ}\) north of east. What is the kinetic energy of the iceboat at the end of that \(8.0 \mathrm{~m} ?\)

A constant force of magnitude \(10 \mathrm{~N}\) makes an angle of \(150^{\circ}\) (measured counterclockwise) with the positive \(x\) direction as it acts on a \(2.0 \mathrm{~kg}\) object moving in an \(x y\) plane. How much work is done on the object by the force as the object moves from the origin to the point having position vector \((2.0 \mathrm{~m}) \hat{\mathrm{i}}-(4.0 \mathrm{~m}) \hat{\mathrm{j}}\) ?

If a ski lift raises 100 passengers averaging \(660 \mathrm{~N}\) in weight to a height of \(150 \mathrm{~m}\) in \(60.0 \mathrm{~s}\), at constant speed, what average power is required of the force making the lift?

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?

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