Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 6 - Section 6.7 - The Dot Product - Exercise Set - Page 793: 54


The work done is 72,000 foot-pounds.

Work Step by Step

Since the crane is vertically lifting the boulder, the angle between the force and direction of motion is $0{}^\circ $. Now it is known, $\mathbf{W}=\left\| \mathbf{F} \right\|\left\| \mathbf{AB} \right\|\cos \theta $ …… (1) As it is given that, $\left\| \mathbf{F} \right\|=6000,\left\| \mathbf{AB} \right\|=12$ and $\theta =0{}^\circ $ …… (2) Therefore, use (2) in (1). So, $\begin{align} & \mathbf{W}=\left( 6000 \right)\left( 12 \right)\cos \left( 0{}^\circ \right) \\ & \mathbf{W}=72000 \end{align}$
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