Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 4 - Dynamics: Newton's Laws of Motion - Problems: 13

Answer

The thief could accelerate downward (not as fast as in free fall), letting the tension in the sheets be less than the thief’s weight.

Work Step by Step

The maximum tension in the sheets is (58 kg)(g) = 568.4 N. Apply Newton’s second law to the thief. Choose up to be the positive direction. $$\Sigma F=F_t – mg = ma$$ $$a = \frac{ F_t-mg}{m} =\frac{568.4 N-(75 kg)(9.80 \frac{m}{s^{2}})}{75 kg} \approx -2.2 \frac{m}{s^{2}}$$ The answer is rounded to 2 significant figures. The negative sign confirms that the acceleration is downward. The weight exceeds the tension, so the thief is moving downward vertically, and speeding up.
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