Book cover for Physics

Physics

John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler

ISBN #9781118486894

10th Edition

2,562 Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This section integrates the concepts of impulse and momentum to describe how time-varying forces affect the motion of objects. The impulseā€“momentum theorem provides a direct way to relate force and contact time to changes in momentum, while the conservation of momentum is a fundamental principle used to analyze collisions. Whether analyzing elastic or inelastic interactions or calculating the center of mass, these concepts are vital for predicting motion in a wide range of physical systems.

Learning Objectives

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Key Concepts

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DEFINITION

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Example Problems

Example 1

A 46-kg skater is standing still in front of a wall. By pushing against the wall she propels herself backward with a velocity of 21.2 m/s. Her hands are in contact with the wall for 0.80 s. Ignore friction and wind resistance. Find the magnitude and direction of the average force she exerts on the wall (which has the same magnitude as, but opposite direction to, the force that the wall applies to her).

Example 2

A model rocket is constructed with a motor that can provide a total impulse of $29.0 \mathrm{N} \cdot \mathrm{s}$ The mass of the rocket is 0.175 kg. What is the speed that this rocket achieves when launched from rest? Neglect the effects of gravity and air resistance.

Example 3

Before starting this problem, review Conceptual Example 3. Suppose that the hail described there bounces off the roof of the car with a velocity of 115 m/s. Ignoring the weight of the hailstones, calculate the force exerted by the hail on the roof. Compare your answer to that obtained in Example 2 for the rain, and verify that your answer is consistent with the conclusion reached in Conceptual Example 3.

Example 4

In a performance test, each of two cars takes 9.0 s to accelerate from rest to 27 m/s. Car A has a mass of 1400 kg, and car B has a mass of 1900 kg. Find the net average force that acts on each car during the test.

Example 5

A volleyball is spiked so that its incoming velocity of $+4.0 \mathrm{m} / \mathrm{s}$ is changed to an outgoing velocity of $-21 \mathrm{m} / \mathrm{s}$. The mass of the volleyball is 0.35 kg. What impulse does the player apply to the ball?
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Step-by-Step Explanations

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Common Mistakes

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