al physics - speed vs velocity

it can.first,speed is a scalar and velocity is a vector
it means it has no displacement
if a car travel 50m forward for 10sec and travel 50m backward for 10sec
speed=travel distance/time
100/40=2.5 per second
velocity=displacement/time=0/40=0

2009-08-24 16:12:14 補充：
你信上邊的好點,HAHAHA!!

2009-08-24 16:13:58 補充：
你的是AVERAGE的,我就對

This statement "a body can have speed but zero velocity" is generally NOT true.
Speed is the magnitude of the velocity, which is a vector and has both magnitude and direction. A zero instantaneous velocity should have zero magnitude. A non-zero instantaneous velocity should have non-zero magnitude (speed).
The statment is only true for "mean speed" and "mean velocity". An object can have zero mean velocity (due to zero displacement), but non-zero mean speed.