A diver performs a dive from a platform which is 10m high. She jumps vertically upwards at 3 m/s.
What is the time she takes to reach the water surface.
Take g=10m/s and neglect air resistance
Physics Velocity
2010-04-10 9:08 pm
回答 (2)
2010-04-10 9:20 pm
✔ 最佳答案
By v=u+at0=3-10t (take upward as positive)
t=0.3s
by v^2=u^2+2as
-9=2x(-10)x s
s= 0.45m
so the highest height is 10.45m
s= ut+ 1/2at^2
10.45=0+5t^2
t=1.44568
so the time needed is 1.44568+0.3
=1.75s (cor to 3 sig. figs)
參考: me
2010-04-10 9:45 pm
Actually, the calculation can be simpler.
Use equation of motion: s = ut + (1/2).a.t^2
with u = 3 m/s, a = -g(= -10 m/s2), s = -10 m, t = ?
hence, -10 = 3t + (1/2).(-10).t^2
i.e. 5t^2 -3t - 10 = 0
solve for t and gives t = 1.75 s or - 1.15 s (rejected)
The time taken is thus 1.75 s
Use equation of motion: s = ut + (1/2).a.t^2
with u = 3 m/s, a = -g(= -10 m/s2), s = -10 m, t = ?
hence, -10 = 3t + (1/2).(-10).t^2
i.e. 5t^2 -3t - 10 = 0
solve for t and gives t = 1.75 s or - 1.15 s (rejected)
The time taken is thus 1.75 s
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