Very urgent question

用戶85377

2010-03-28 1:05 am

Explain it very clearly.

1. Billy and Lily want to move from one end to the other end of a straight long track. Both of them start at the same time and at the same point. Billy runs with a uniform velocity of 8 ms^-1 in the first half-time and then walks with a uniform velocity of 4ms^1 in the next half-time. Lily walks with uniform velocity of 4 ms^-1 in the first half-time and then runs with a uniform velocity of 8 ms^-1 in the next half-time. Is the statement correct? Why or why not?

Statement: Billy and Lily reach the end of the track at the same time.

回答 (1)

天同

2010-03-28 8:58 am

✔ 最佳答案

The statement may not be correct.

Velocity is a vector quantity. The question only specifies the magnitudes of the velocity of Billy and Lily, but not their directions.
Since the track is a straight long one, there are two directions. Billy could first go towards the end-point in the first half-time, and then reverses his direction in the second half-time. Hence, Billy may not reach the end-point at the same time as Lily.

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