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Chapter 9: Q.60 (page 230)

A 90kg firefighter needs to climb the stairs of a 20m-tall building while carrying a 40kg backpack filled with gear. How much power does he need to reach the top in 55s?

Short Answer

Expert verified

The power need to reach the top in55sis460W

Step by step solution

01

Content Introduction

Power is the rate of doing work. It is calculated as

P=Wt

Work done is the dot product of force and displacement.

W(F鈫�)=F鈫�.d鈫�W(F鈫�)=Fdcos胃

Substitute mgforFgand 180掳for 胃.

W(F鈫�)=mgd(cos180掳)W(F鈫�)=-mgd

Hence, work done by firefighter is equal to negative of potential energy.

02

Content Explanation

The power need to reach the top in 55sis

P=mgdtP=(130kg)(9.8m/s)(20m)55sP=460W

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