## College Physics (4th Edition)

Published by McGraw-Hill Education

# Chapter 6 - Problems - Page 231: 76

#### Answer

(a) The force exerted by the air is 20 N (b) The cyclist's speed will be $6.67~m/s$

#### Work Step by Step

(a) Since the cyclist is moving at a constant speed, the force exerted by the air must be equal in magnitude to the force pushing the cyclist forward. We can find the magnitude of the force: $P = F~v$ $F = \frac{P}{v}$ $F = \frac{120~W}{6.0~m/s}$ $F = 20~N$ The force exerted by the air is 20 N (b) We can find the cyclist's speed when the force exerted by the air is 18 N: $F~v = P$ $v = \frac{P}{F}$ $v = \frac{120~W}{18~N}$ $v = 6.67~m/s$ The cyclist's speed will be $6.67~m/s$

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