dust to dust

Quote:

If dust falls at approximately .5meters per second off a 200ft high wall. the wind is blowing at a 45 degree angle up with a force of 1 meter an hour. when does the dust hit the ground?

The point of this problem is to find out the resulting downwards velocity of the dust given that the wind is blowing at an upward angle.
Note that since we are not told the mass of the dust it is assumed we can neglect the force of gravity for this problem and that the particles velocity will be constant.

The velocity upwards that the wind gives the dust is 1 m/h * sin(45 degrees) = sqrt(2)/2 m/h = sqrt(2)/7200 m/s; (3600 seconds to an hour)

The upwards velocities just add so the resulting velocity is

0.5 + sqrt(2)/7200 m/s = (3600 + sqrt(2))/7200 m/s ~ 0.5 m/s; (note the wind has almost no effect, are you sure it wasn't 1 m/s windspeed?)

The time it will take to fall 200 ft is 200 feet divided by the velocity (in feet/second, we'll have to convert from m/s to ft/s)

There are about 3.05 feet/meter so the velocity in feet/s is 0.5m/s * 3.05 ft/m = 1.525 ft/s

So the time is now given by 200ft/1.525 ft/s = 131.15 seconds

mathguy88:

[size=200][center][color=#808000]If dust falls at approximately .5meters per second off a 200ft high wall. the wind is blowing at a 45 degree angle up with a force of 1 meter an hour. when does the dust hit the ground?
[/center][/size][/color]

Hi mathguy88,
You know, you have presented this question like as if you are screaming at us. It is a little offensive. It is also harder to read.
Please do not get carried away with your presention like this.
[size=200]WE ARE NOT DEAF. [/size]

[size=200]I think that you owe Rom a big thank you and an apology.[/size]

Also, Vector Velocity is just one of many titles that would have been better. If you name your post appropriately it often means that the right respondent spots it quicker and more easily. It also means that the post is more useful to other people who are trying to learn the same category of mathematics. (They can find it when they search)

Melody

There is no reason to write that big. You might want to thank Rom for his help.