maths.. 15pts!
2009-11-06 7:30 am
An object is thrown into the air from the ground level. By the time it reaches a height of 100 meters, it is moving at 10 meters per second. How long did it take to get to that height? How fast was it orignally thrown? What is the greatest height it reaches? When does it hit the ground?
回答 (1)
2009-11-06 7:58 am
✔ 最佳答案
Let the initial velocity be v m/sv^2 - 10^2 = 2 * 10 * 100
v^2 = 2000 + 100 = 2100
v = 45.83 m/s
It was at 45.83m/s originally
10 = 45.83 - 10t
10t = 35.83
t = 3.583
It takes 3.583 seconds to reach there
s = 45.83t - (1/2)(10)t^2
= 45.83t - 5t^2
s = 0=> t = 0 or t = 9.165
It will hit the ground at 9.165s after being thrown
Maximum height is 45.83(9.165/2) - 5(9.165/2)^2 = 105m
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https://hk.answers.yahoo.com/question/index?qid=20091105000051KK01715