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p02_018

# Fundamentals of Physics,Vol 1 (Chapters 1 - 20)

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18. We use Eq. 2-2 (average velocity) and Eq. 2-7 (average acceleration). Regarding our coordinate choices, the initial position of the man is taken as the origin and his direction of motion during 5 min t 10 min is taken to be the positive x direction. We also use the fact that ∆ x = v t 0 when the velocity is constant during a time interval ∆ t 0 . (a) Here, the entire interval considered is ∆ t =8 2 = 6 min which is equivalent to 360 s, whereas the sub-interval in which he is moving is only ∆ t 0 =8 5 = 3 min = 180 s. His position at t =2m in is x = 0 and his position at t = 8 min is x = v t 0 =(2 . 2)(180) = 396 m. Therefore, v avg = 396 m 0 360 s =1 . 10 m / s . (b) The man is at rest at t = 2 min and has velocity v =+2 . 2 m/s at t = 8 min. Thus, keeping the answer to 3 signiFcant Fgures, a avg = 2 . 2m / s 0 360 s =0 . 00611 m / s 2 . (c) Now, the entire interval considered is ∆ t =9 3 = 6 min (360 s again), whereas the sub-interval
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