## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

Published by Pearson

# Chapter 7 - Newton's Third Law - Exercises and Problems - Page 178: 19

#### Answer

The person needs to pull on the rope with a force of 245 N

#### Work Step by Step

We can assume that the pulley and the rope are massless. If the crate is lowered at a steady speed, then the person's force on the rope must be equal in magnitude to the weight of the crate. Then the net force on the crate is zero and the crate's acceleration is zero. $F = mg$ $F = (25~kg)(9.80~m/s^2)$ $F = 245~N$ The person needs to pull on the rope with a force of 245 N.

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