John releases ball A at time t=0 from rest at a position 7m above the ground. At the same time, ball B projected vertically upwards from the ground with an initial speed of 8m/s.
1. When will the balls meet in air?
2. What height will the balls meet in air?
物理PHY
2015-07-20 5:11 am
回答 (2)
2015-07-20 6:40 am
✔ 最佳答案
1.Take g = 10 m s⁻²
Take downward quantities as positive.
Let h m above the ground be the height of the balls meet in air.
Ball A :
s = (7 ‒ h), u = 0, g = 10 m s⁻²
s = ut + (1/2)at²
7 ‒ h = (1/2)(10)t²
7 ‒ h = 5t² ...... [1]
Ball B :
s = ‒h, u = ‒8 m s⁻¹, g = 10 m s⁻²
s = ut + (1/2)at²
‒h = (‒8)t + (1/2)(10)t²
‒h = ‒8t + 5t² ...... [2]
[1] ‒ [2]：
7 = 8t
Time taken, t = 0.875 s
2.
Put t = 0.875 s into [1] :
7 ‒ h = 5(0.875)²
The height that the balls will meet, h = 3.17m
2015-07-20 6:54 am
收錄日期: 2021-04-16 17:08:02
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https://hk.answers.yahoo.com/question/index?qid=20150719000051KK00045