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Chapter 7: Q8 CQ (page 258)

Does the work you do on a book when you lift it onto a shelf depend on the path taken? On the time taken? On the height of the shelf? On the mass of the book?

Short Answer

Expert verified

The work done on a book when it is lifted onto a shelf doesn’t depend on the path and on the time taken, but it depends on the height of the shelf and the mass of the book.

Step by step solution

01

Step 1: Definition of Concept

Potential energy: The work done on the object to displace it against the conservative gravitational force is stored in the form of potential energy which is given as,

W=P.E.=mg(h2-h1)

(1.1)

Here, m is the mass of an object, g is the acceleration due to gravity, h2is the final height of the object, and h1is the initial height of the object.

02

Explain the work done on a book when it is lifted

From equation (1.1), it is clear that the work done on a book when it is lifted onto a shelf depends on the height of the self and on the mass of the book and is independent of the path and the time taken.

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Most popular questions from this chapter

Using energy considerations, calculate the average force a 60.0-kg sprinter exerts backward on the track to accelerate from 2.00 to 8.00 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him.

Suppose the ski patrol lowers a rescue sled and victim, having a total mass of 90.0 kg, down a 60.0º slope at constant speed, as shown in Figure 7.37. The coefficient of friction between the sled and the snow is 0.100.

(a) How much work is done by friction as the sled moves 30.0 m along the hill?

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(d) What is the total work done?

Figure 7.37 A rescue sled and victim are lowered down a steep slope.

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(a) Calculate the force exerted by a boxing glove on an opponent’s face, if the glove and face compress 7.50 cm during a blow in which the 7.00-kg arm and glove are brought to rest from an initial speed of 10.0 m/s.

(b) Calculate the force exerted by an identical blow in the gory old days when no gloves were used and the knuckles and face would compress only 2.00 cm.

(c) Discuss the magnitude of the force with glove on. Does it seem high enough to cause damage even though it is lower than the force with no glove?

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Figure 7.44

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