力學題.花你幾十秒

[S]Mangoray

答案是B,而不是C
為什麼?

Zend

speed = total distance/ time

total distance =2x

time = x/4 +x/6

speed = 2x /(x/4+x/6) = 2x / [(6x+4x)/24] = 48x/10x =4.8 ms^-1

cla981085

let total distance = 2d
total time taken = d/4 + d/6

average speed = 2d/(d/4 + d/6)
                     = 4.8ms^-1

kkuukkoo

let total distance = 2d
total time taken = d/4 + d/6

average speed = 2d/(d/4 + d/6)
                     = 4.8ms^-1
cla981085 發表於 13-9-2009 10:38

為了方便
個d可以任let@@