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... 67.5 ° (north of east), â 2.90 = tan ă or 22.5° east of due north 6 To emphasize the fact that the velocity is a function of time, we adopt the notation v(t) for dx / dt (a) Eq 4-1 0 leads to... be written as ∆ r = r − ro = ( 56.6 ∠ 135 ° ) in terms of the magnitude-angle notation & (c) The magnitude of vavg is simply the magnitude of the displacement divided by the time (∆t = 30 s) Thus,... 4-8 shows that vavg points in the same direction as ∆ r , i.e, 135° ( 45° north of due west) (e) Using Eq 4-1 5, we have & & v − vo & aavg = = 0.333i + 0.333j ∆t in SI units The magnitude of