## College Physics (4th Edition)

Published by McGraw-Hill Education

# Chapter 3 - Problems - Page 118: 105

#### Answer

(a) The average speed across each synapse is $1.0\times 10^{-3}~m/s$ (b) It takes $20.2~ms$ for the signal to reach the brain. (c) The average speed is $99.0~m/s$

#### Work Step by Step

(a) We can find the average speed $v_{ave}$ across each synapse: $v_{ave} = \frac{d}{t} = \frac{100\times 10^{-9}~m}{1.0\times 10^{-4}~s} = 1.0\times 10^{-3}~m/s$ The average speed across each synapse is $1.0\times 10^{-3}~m/s$ (b) We can find the time $t$ across each sensory neuron: $t = \frac{d}{v} = \frac{1.0~m}{100~m/s} = 0.010~s = 10.0~ms$ We can find the total time: $2\times 10.0~ms~+~2\times 0.10~ms = 20.2~ms$ It takes $20.2~ms$ for the signal to reach the brain. (c) We can find the average speed: $v_{ave} = \frac{d}{t} = \frac{2.0~m+200\times 10^{-9}~m}{0.0202~s} = 99.0~m/s$ The average speed is $99.0~m/s$

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