In the following graph，the velocity of an object as it moves along a horizontal straight line（水平直線）is plotted against time．（一個(gè)物體在水平直線上運(yùn)動(dòng)，其速度隨時(shí)間的變化如圖所示）
精英家教網(wǎng)
（1）The distance traveled by the object during the frist 6seconds in
 
meters．（物體在前6s內(nèi)的位移是多少）
（2）The average speed of the object during the first 8seconds is in meters per second
 
．（物體在前8s內(nèi)的平均速率是多少）
分析：（1）速度時(shí)間圖象與時(shí)間軸所圍的“面積”表示位移，由幾何知識(shí)求解位移；
（2）先求出位移，再由平均速率公式
.
v
=
S
t
求平均速率．
解答：解：（1）速度時(shí)間圖象與時(shí)間軸所圍的“面積”表示位移，則物體在前6s內(nèi)的位移是
  x=
1
2
×（2+6）×4m=16m
（2）物體在前8s內(nèi)的位移為：
x′=
1
2
×（2+8）×4=20m
由于前8s內(nèi)物體做單向直線運(yùn)動(dòng)，路程等于位移的大小，則前8s內(nèi)路程為S=x′=20m
則平均速率
.
v
=
S
t
=
20
8
=2.5m/s
故答案為：16，2.5m/s．
點(diǎn)評(píng)：解答本題關(guān)鍵掌握速度圖象的物理意義：面積表示位移，以及平均速率公式．
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