mechanics

Question

1st:The magnitude of average velocity of a moving object is always its average speed
2nd:The magnitude of instantaneous velocity of a moving object is its instantaneous spped

Why both statements are wrong?

Answer 1

1st:The magnitude of average velocity of a moving object is always its average speed
2nd:The magnitude of instantaneous velocity of a moving object is its instantaneous speed

第一句)
velocity(速度)是向量。speed(速率)是無向量，兩者不相同。
例如以運動會的400m賽跑為例，
50s跑完400m，
平均速度是0，因為位移為0。
平均速率為400/50= 8ms-1

第二句)應該是正確。