Đáp án:
a. Ta có:
$s = v_0.t + \dfrac{at^2}{2}$
Mà: $s = 10cm = 0,1m$; $v_0 = 0$
Suy ra:
$a = \dfrac{s}{t^2} = \dfrac{0,1}{1^2} = 0,1 (m/s^2)$
b. $v_0 = 18km/h = 5m/s$
$s_4 = v_0.t + \dfrac{at^2}{2} = 5.4 + \dfrac{a.4^2}{2} = 8a + 20 (m)$
$s_5 = v_0.t + \dfrac{at^2}{2} = 5.5 + \dfrac{a.5^2}{2} = 12,5a + 25 (m)$
$s_5 - s_4 = 5,9 \Rightarrow 12,5a + 25 - (8a + 20) = 5,9$
$\Rightarrow 4,5a + 5 = 5,9 \Rightarrow a = 0,2 (m/s^2)$
c. $v_0 = 18km/h = 5m/s$
$s_3 = v_0.t + \dfrac{at^2}{2} = 5.3 + \dfrac{a.3^2}{2} = 4,5a + 15 (m)$
$s_4 = v_0.t + \dfrac{at^2}{2} = 5.4 + \dfrac{a.4^2}{2} = 8a + 20 (m)$
$s_4 - s_3 = 12 \Rightarrow 8a + 20 - (4,5a + 15) = 12$
$\Rightarrow 3,5a + 5 = 12 \Rightarrow a = 2 (m/s^2)$
d.
$v_0 = 18km/h = 5m/s$
$s_4 = v_0.t + \dfrac{at^2}{2} = 5.4 + \dfrac{a.4^2}{2} = 8a + 20 (m)$
$s_5 = v_0.t + \dfrac{at^2}{2} = 5.5 + \dfrac{a.5^2}{2} = 12,5a + 25 (m)$
$s_5 - s_4 = 5,45 \Rightarrow 12,5a + 25 - (8a + 20) = 5,45$
$\Rightarrow 4,5a + 5 = 5,45 \Rightarrow a = 0,1 (m/s^2)$
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