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Chapter 7: Q6 CQ (page 258)

When solving for speed in Example 7.4, we kept only the positive root. Why?

Short Answer

Expert verified

We keep only the positive root of the speed because speed cannot be negative.

Step by step solution

01

Step 1: Definition of Concept 

Speed: Meters per second are used to measure speed (SI). As a result, it is given by dividing distance by time. S = d/t is the formula.

02

Speed.

The speed is defined as the rate of change in the distance of an object.

V=St

Here, s is the distance covered by the object in time t.

03

Speed cannot be negative.

Since both distance and time cannot be negative. Therefore, the speed of the object can never be negative.

The negative sign is used only to indicate the direction of the object’s motion.

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Most popular questions from this chapter

What is conservative force?

(a) How long can you rapidly climb stairs\(\left( {116/{\rm{min}}} \right)\)on the\(93.0{\rm{ kcal}}\)of energy in a\(10.0 - {\rm{g}}\)pat of butter?

(b) How many flights is this if each flight has\(16\)stairs?

(a) Find the useful power output of an elevator motor that lifts a \(2500 - {\rm{kg}}\) load a height of \(35.0{\rm{ m}}\) in \(12.0{\rm{ s}}\), if it also increases the speed from rest to \(4.00{\rm{ m}}/{\rm{s}}\). Note that the total mass of the counterbalanced system is \(10,000{\rm{ kg}} - \)so that only \(2500{\rm{ kg}}\) is raised in height, but the full \(10,000{\rm{ kg}}\) is accelerated.

(b) What does it cost, if electricity is \(\$ 0.0900{\rm{ per kW}} \cdot {\rm{h}}\)?

A pogo stick has a spring with a force constant of 2.50×104N/m, which can be compressed12.0cm. To what maximum height can a child jump on the stick using only the energy in the spring, if the child and stick have a total mass of40.0kg? Explicitly show how you follow the steps in the Problem-Solving Strategies for Energy.

Suppose a car travels\(108{\rm{ km}}\)at a speed of\(30.0\,{\rm{m}}/{\rm{s}}\), and uses\(2.0{\rm{ gal}}\)of gasoline. Only\(30\% \)30% of the gasoline goes into useful work by the force that keeps the car moving at constant speed despite friction. (See Table 7.1 for the energy content of gasoline.)

(a) What is the magnitude of the force exerted to keep the car moving at constant speed?

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