velocity 問題

Average velocity is obtained by
final displacement / time taken
however, the actual velocity may be changing within that period of time.

for example,
a racer takes part in a 400 m race. After finishing the race (400 m, a cycle), his final displacement is zero, so his average velocity is zero.

however, the racer of course have velocity at different time!!
that velcoity which at a specific time is called instantaneous velocity.

instantaneously velocity can be found by using equations of motion:
v = u + at
v^2 - u^2 = 2as
s = ut + (1/2)at^2
s = (u + v)t/2


2007-10-31 01:16:24 補充：
initial velocity=its velocity at the begining, i.e. with a specific time, so it is instantaneous velocity.for velocity is 50, if its velcoity unchange, aver. velocity=instantaneous velocity=50if it accelerates, then 50 is only the initial velocity, so is instantaneous velocity.