A girl standing on a bridge throws a stone vertically downward with an initial velocity of 10 m/s into the river below. If the stone hits the water 4 seconds later, what is the height of the bridge above the water?
2007-08-03 08:15:35 · 8 answers · asked by shall_i 1 in Science & Mathematics ➔ Mathematics
40m =]
2007-08-03 08:19:09 · answer #1 · answered by Anonymous · 0⤊ 0⤋
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2016-11-11 03:15:40 · answer #2 · answered by ? 4 · 0⤊ 0⤋
A simple physics question.
S = Vo*t + 1/2 a*t^2
read distance = Initial Velocity times Time plus 1/2 acceleration times Time squared.
If there were no acceleration, then Velocity * time = 40 would be correct. But the rock was thrown down and is being acted on by gravity (32.2 ft/sec^2 or 9.8 m/sec^2)
Equation becomes
S = (10)*4 + (1/2)*9.8*(4^2) = 118.4 meters.
2007-08-03 08:31:06 · answer #3 · answered by Scott W 3 · 0⤊ 0⤋
Those who said 40m are failing to take into account acceleration due to gravity, for which I use the approximation 10 ms^-2
Then use Newton's equation of motion s = ut+1/2 at^2
where s = distance (to find)
u = initial velocity (10 m/s)
t = time
a = acceleration (10 ms^-2)
plug in numbers and get 120m
2007-08-03 08:29:21 · answer #4 · answered by Nick J 4 · 0⤊ 0⤋
a = dv/dt = -32
v = -32t+C When t = 0 v = -10m/s, so C= 10
v=ds/dt = -32t -10
s = -16t^2-10t + C When t = 0 s= 0 so C=0
s= -16t^2 -10t
When t = 4, s = -256 -40 = -296 feet
The bridge is 296 m above the water
2007-08-03 08:32:40 · answer #5 · answered by ironduke8159 7 · 0⤊ 0⤋
40 meters
2007-08-03 08:19:06 · answer #6 · answered by Happy 3 · 0⤊ 0⤋
40 meters... 4x10=40
2007-08-03 08:45:00 · answer #7 · answered by Benjamin S 2 · 0⤊ 0⤋
i dont know
2007-08-03 08:22:24 · answer #8 · answered by Anonymous · 0⤊ 0⤋