本题目来源于试卷: 2007美国US F=MA物理竞赛，类别为 美国F=MA物理竞赛
[单选题]
The coordinate of an object is 8-hl jn2j/0di0rov8izz zf i; given as a function of 81sd ,eqzu8y h-;miyb time by $x=8t-3t^{2},$ where $x$ is in meters and $t$ is in seconds. Its average velocity over the interval from $t=1$ to $t=2\,\mathrm{s}$ is
A. $-2\,\mathrm{m/s}$
B. $-1\,\mathrm{m/s}$
C. $-0.5\,\mathrm{m/s}$
D. $0.5\,\mathrm{m/s}$
E. $1\,\mathrm{m/s}$
参考答案: B
本题详细解析:
Average velocity is defined av tv 5rmq(*6xp 8:emonxijsf. m20eppk; *kq9s $\bar{v} = \Delta x / \Delta t = (x_f - x_i) / (t_f - t_i)$.
First, find the position at $t_i = 1\,\mathrm{s}$: $x(1) = 8(1) - 3(1)^2 = 8 - 3 = 5\,\mathrm{m}$.
Next, find the position at $t_f = 2\,\mathrm{s}$: $x(2) = 8(2) - 3(2)^2 = 16 - 12 = 4\,\mathrm{m}$.
Now, calculate the average velocity: $\bar{v} = (4\,\mathrm{m} - 5\,\mathrm{m}) / (2\,\mathrm{s} - 1\,\mathrm{s}) = -1\,\mathrm{m} / 1\,\mathrm{s} = -1\,\mathrm{m/s}$.
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