A stone is thrown vertically upwards from the ground with a speed of 20m/s.
a)Calculate the maxium height reached.
b)How long does it take to return to the ground?
Motion uder gravity
2008-08-21 7:58 am
回答 (1)
2008-08-21 10:17 am
✔ 最佳答案
Take all upward quantities as +ve, and all downward quantities as -ve.
Take g = 10 m/s2
(If take g = 9.8 m/s2 or 9.81 m/s2, the answers would be slightly different.)
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a)
u = 20 m/s
v = 0
a = g = -10 m/s2
v2 = u2 + 2as
0 = (20)2 + 2(-10)s
400 - 20s = 0
s = 20
Maximum height = 20 m
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b)
u = 20 m/s
s = 0
a = g = -10 m/s2
s = ut + (1/2)at2
0 = (20)t + (1/2)(-10)t2
20t - 5t2 = 0
4t - t2 = 0
t(4 - t) = 0
t ≠ 0, hence t = 4
Time taken = 4 s
=
收錄日期: 2021-04-23 23:07:01
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