physics question

[akorcovelos]

posted this on E30tech also, lets see if we get the same solution!

ok, lets see who can solve this.

knowns are distance of fall (2') force of impact (500 lbs).

I need to know the mass of the falling object to generate the 500 lb impact force when dropped from 2'.

edit: please show your work!

[mrsleeve]

force = mass x acceleration, acceleration is a constant at 9.8m per second^2

for give me if that dosent help its been a long time since physics.

[akorcovelos]

force = mass x acceleration, acceleration is a constant at 9.8m per second^2

for give me if that dosent help its been a long time since physics.

Right, I'm having trouble solving for m with the knowns being a=9.8m per s^2 and F=500 lbs

[uofom3]

500 = m * 9.8mps^2

m = (500)/ (9.8mps^2)

that seemed really easy... maybe I'm missing something

[bwanac]

since we are doing it in english units or whatever its called, g = 32.2 ft per sec^2

[akorcovelos]

since we are doing it in english units or whatever its called, g = 32.2 ft per sec^2

right, I should stop mixing the units like that , it can be confusing.

[bwanac]

is that what you wanted? because it seems you need to know how long the impact is to understand the force.

[fretburnr]

if you use F=ma,

500 lbf (pounds force) = 2,224.111 Newtons

2,224.111 = m * 9.8 m/s^2
2,224.111 / 9.8 = m
226.95 = m

226.95 kg ~= 500 lb. duh, that's what we started with.

you need to look at it as a momentum based collision. i'll be back in 5, gotta meeting at work.

[StereoInstaller1]

6 replies and no treadmill?

[uofom3]

^
r3v has recently made a turn for the sane/helpful. It's pretty strange...

[bwanac]

if you use F=ma,

500 lbf (pounds force) = 2,224.111 Newtons

2,224.111 = m * 9.8 m/s^2
2,224.111 / 9.8 = m
226.95 = m

226.95 kg ~= 500 lb. duh, that's what we started with.

you need to look at it as a momentum based collision. i'll be back in 5, gotta meeting at work.

yup. P=mv and F=ma where a=dv/dt.

[fretburnr]

scratch that, it's not momentum. I just worked it out and it comes out the same, then BLAO! lightbulb, and memory from physics class.

Pounds isn't a measure of mass, it is a measure of force at normal G acceleration.

500lb impact requires a 500lb object. I just proved it with math in the prev. post.

[fretburnr]

further proof:

f= m * (dv/dt)

v^2 = Vo^2 + 2 a (x-Xo)
v^2 = 0 + (2 * 9.8 * 0.6096m)
v^2 = 11.948
v = 3.457

v = Vo + a t
3.457 = 0 + 9.8 t
.0353 = t

F = m * (3.457 / .0353)
2224.111 N = m * 97.93
226.94 kg = m

226.94 kg ~= 500lb

[akorcovelos]

So your telling me that I need to drop a 500 lb weight from 2' to generate 500 lbs of impact on an object? Gravity wouldn't increase the force?

[LivingLegend06]

lol guys, you all suck at physics.

The object does not simply create a force on impact, it needs to come to rest over some distance over which it will have an acceleration.

If this is some kind of homework problem its a trick question and just say that the object has a mass of (500/32.2) slugs.