A diver springs upwards with a speed of 2.5ms^-1 from a 3m board.
Find the velocity of the diver juz before he reaches the water.
f.4 phys..如果上返去再落番尼,,,錦a係-10定10呀?
2008-10-18 7:28 pm
回答 (2)
2008-10-18 8:25 pm
✔ 最佳答案
Use equation of motion,u = 2.5 m/s, a = -g (=-10 m/s2), s = -3 m, v =?
using v^2=u^2 + 2.a.s
v^2 = 2.5^2 + 2x(-10)x(-3) (m/s)^2 = 66.25 (m/s)^2
i.e. v = -8.14 m/s
2008-10-18 10:41 pm
take upwards as positive
u=2.5 a=-10 v=0 s=?
v^2=u^2+2as
0=2.5^2+2(-10)s
s=0.3125m
(this is the upwards journey)
u=0 a=-10 s=0.3125+3=3.3125 v=?
v^2=u^2+2as
v^2=2(-10)(-3.3125)
v=8.139(rej.) or -8.139ms^-1
(this is the downwards journey)
so the velocity is -8.139ms^-1
u=2.5 a=-10 v=0 s=?
v^2=u^2+2as
0=2.5^2+2(-10)s
s=0.3125m
(this is the upwards journey)
u=0 a=-10 s=0.3125+3=3.3125 v=?
v^2=u^2+2as
v^2=2(-10)(-3.3125)
v=8.139(rej.) or -8.139ms^-1
(this is the downwards journey)
so the velocity is -8.139ms^-1
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