Rectilinear motion 問題
2011-07-14 2:19 am
A bag is dropped from a balloon that is 300m above the ground and rising at 13m/s. For the bag, find the time before it hits the ground.
回答 (1)
2011-07-14 3:40 am
✔ 最佳答案
Use equation of motion: s = ut + (1/2)at^2with s = -300 m, u = 13 m/s, a = -g (=-10 m/s^2), t = ?
hence, -300 = 13t + (1/2).(10)t^2
i.e. 5t^2 -13t -300 = 0
solve for t gives t = 9.15 s or - 6.55 s (rejected)
Therefore, it takes 9.15 s for the bag to reach the ground.
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https://hk.answers.yahoo.com/question/index?qid=20110713000051KK00848