(A)
s{ t } = (¼)t² + 2t + 1 ... differentiate to get velocity versus time
v{ t } = (½)t + 2 ... linearly increases with time
(1)
Vavɢ{ a→b } = [ v{ b } + v{ a } ] ⁄ 2
Vavɢ{ 1→3 } = [ v{ 3 } + v{1 } ] ⁄ 2
Vavɢ{ 1→3 } = [ (½)(3) + 2 + (½)(1) + 2 ] ⁄ 2
Vavɢ{ 1→3 } = 3 m/sec
(II) and (III) are done the same way.
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(B)
v{ t } = (½)t + 2
v{1 } = (½)(1) + 2
v{1 } = 2.5 m/sec