Any help?

[Kilivek2.0]

i've been entering answers into the fucking problem for about an hour now and can't get a damn break...

anyone know their shit so they can save the day?

[brekk]

need more info, what period time are we talking, here. You have beginning, and ending velocity, but not a duration for the change.

I see the small 25s up in the formula

Acceleration = Delta Velocity / Delta Time

A = 200 - 18 / 25

A = 182 / 25 = 7.28m/s^2

And acceleration can't be negative. Acceleration is not a directional force.

Edit: Fuck Physics II and Gauss, but Physics I was my bitch.

[Millie]

Originally Posted by brekk

And acceleration can't be negative. Acceleration is not a directional force..

I haven't taken a Physics class since freshman year in college, and it wasn't my specialty, but I seem to remember that negative acceleration = slowing down. So it can be negative. And logically, I would think that one's acceleration just after opening a parachute would be slightly negative. Remember that acceleration is not velocity; it is the rate of change in velocity. During that brief moment when you shift from free fall to parachute, you decelerate (i.e., slow down) a tiny bit. So I would think the answer would be negative here.

Also found this on Google, which kind of confuses things a bit further:

An object in free fall has a negative acceleration even though it is increasing speed. It is negative because the object is moving in a negative direction.

So, umm, I dunno. I'll stop dumb blonding my way through a Physics thread now, but I just wanted to share this stuff! Take it with a grain of salt, because like I said, I really don't know what I'm talking about on this subject.

[Ninajrr]

Acceleration is not a vector, and thus should not be negative.

The only thing I can think of here is that your acceleration due to gravity changes with your distance, but that should be negligible.

What are you studying? That is always a good indication of what they are asking you to do. Are you given any more information or is this it?

[Kilivek2.0]

acceleration can be negative

velocity increasing in negative direction = negative acceleration.

7.28 = wrong btw.

[Malakriss]

Acceleration is the derivative of velocity which is the derivative of position.
Acceleration can be negative specifically because it isn't a vector, it's a rate of change.

[Kilivek2.0]

back to the oringinal question please?

[Malakriss]

Btw, the speeds are in km/h, while the acceleration requests m/s^2. So the instantenous acceleration is needs to be the same? Convert it.

[Kilivek2.0]

the problem is with his method is that deceleration won't be gradual over 25 seconds like that.

When you open a parachute it's accompanied by rapid jolt deceleration and then slowing down. that's what that equation shows...
However solving for the derivative of that equation at any given time gives a slope of like -2. don't know maybe i'm missing something upon entering it.

[Malakriss]

I hate math... especially at 8am...

200km/h = 200000m/h = 55.555m/s
18km/h = 18000m/h = 5m/s

working on it...

[Malakriss]

d (55.5555 + 50.555e^(-x/25),x,0) = 106.111111

dy/dx (0,106.111) = -2.02222 m/s^2 ???

[Kilivek2.0]

wrong.

same shit i got. i dont know what the deal is.

[Malakriss]

googled the speed of the skydiver, standard conversion is 200km/h = 56m/s

-2.04 is what I got by using 56 + 51e^(-x/25)

try 2.04 or -2.04 just for kicks? I hope you don't have a limited # of tries

[Ironhawk]

Way over my head, but here's my contribution.

[Malakriss]

Logically... you're going from 56m/s to 5m/s or a ~50m/s difference. The average with a 25s drag time has to be around -2 m/s^2 acceleration. The parachute doesn't give you one sudden speed change, it gives a constant air resistance so the acceleration throughout the whole period should be nearly constant, around -2.

Only other suggestion is to assume the answer was derived by an idiot who didn't realize terminal velocity is 0.0 acceleration, so try -9.81 + 2 = -7.81 or -7.82