# Throw that 90lb bag of cement to me... WCGW?

Why would he even try to catch that?

I think the last time this was posted there was more shown - basically I believe they threw down a couple of light things first. He caught them easily and then they sandbagged him with this one. Glad to see he has such a good sense of humor.

Its just a prank bro!! I hope you didn't need your back!

You could launch that bag 300m if you had a trebuchet

It's only gonna bother you the rest of your life bro!

You'll remember this prank forever bro!

90 pounds is 40.8 kilograms. Based on my drunk calculations it's only 136.1 meters. Close enough, upvoted!

You are right, that sweet spot is 90kg over a remarkable distance of 300m.

You could say that he cemented his place in the hospital.

Wow that is seriously fucked. Could have disabled him for life if he was unlucky.

Im not sure how trebuchets actually work but I assume theres a 'sweetspot' when it comes to weight, too light and it won't go far enough, too heavy and it won't go far enough.

I could be wrong though.

It was a social experiment that will be difficult to forget.

Doesn't that mean you could actually throw it further if it's lighter?

Footage from the soccer stadium construction site in Doha.

That is horrible for the back. Horrible.

wrists and elbows too can get fucked on this

90lbs is around 50kgs right? Well where i come from, during construction they do that. They throw the bags of cement down to use. They usually keep the bags on the top floor so its harder for people to steal. They just throw and catch. Nsfw but it works. Saves shitloads of time

Assuming 55lb/25kg, the force required to stop, applied over one meter, is about 490N (the raw kinetic energy) + 245N (the force of gravity). But it's moving fast, so that's a big impulse, so it's really hard.

Here's most of my response from back then.

Where:

v = final velocity v_0 = initial velocity = 0 a = acceleration = 9.81 m/s s = displacement during acceleration = 2 m (rough guess based on distance between roof edge and shoulder level) E_k = W = kinetic energy = work required to stop over displacement necessary to stop m = mass = 55 lb = 24.9 kg d = displacement necessary to stop = 1 m (he has about 1 meter to stop the object to avoid slamming his head into the ground) F = force necessary to stop within the displacement

Thus:

v^2 = 0 + 2as = 2 * 9.81 m/s^2 * 2 m = 39.2 m^2/s^2 E_k = 0.5mv^2 = 0.5 * 24.9 kg * 39.2 m^2/s^2 = 488 kg*m^2/s^2 = 488 J F = W / d = E_k / d = 488 J / 1 m = 488 N = 110 lb-force

So he would have needed to basically deadlift lift double the weight of the sack, and fast.

I thought about this a bit more, and I don't think simply lifting 110 lb is a good comparison, it's a lot harder than that. First of all, you also have to resist the force of gravity throughout the motion, which adds another 55 lb (245 N). The mechanics of the human body and the difference between lifting dead weight probably also make this a lot harder than just "lifting 165 lb".

With spine-tingling results!

Rock solid observation

Ok. Both you and /u/pingu3101 must live on a planet of superior strength. Hiding bags of concrete on roofs so they don't get stolen? Throwing around 80 lb medicine balls? And to think I felt good about myself because I briskly walked 2 miles yesterday.

I think bodies in general will get fucked from this

crossfit

Will a mathematician please do the calculations for us!?

He's gonna need help with both of his arms ripped out of their sockets.

Reminds me of that song, let the bodies hit the floor.

It's closer to 40kg, but you're right - it's not implausible to catch this and I'm not even Mr. Universe - but I do regularly use a 40kg slam ball (medicine ball) at the gym. It's heavy, but not like "OMG DEADLY". Especially at that tiny distance.

Frankly, the dude just doesn't know how to catch or wasn't paying attention.

You just got fired from the trebuchet club. If you don't know the metric system you can use a catapult!

OHSA would like to have a word with you

im so glad we're downvoting this joke now.

Not any more :(

Could have killed him for life. Just use your imagination ffs

It dropped him

And knees and toes

Knees and toes too.

*wheelbarrow

He was looking for a quick way to break both his arms.

Could've easily broken his neck and/or back.

Damn catapulters, THIS IS TREBUCHET TOWN!

I'm sure he's excited to go home to his mother

Ya but how big is the trebuchet?

I just cracked up

And knees and toes

Definitely a plausible theory. There is a wheel barrel in the corner that looks like it's filled with similar sacks but smaller and lighter.

I absolutely don't believe you're casually tossing around 40kg medicine balls around.

Yeah he's way oversteching instead of catching close and using his legs to absorb, poor form for sure. He wouldn't keep up with the cubs.

You couldn't. Mystery solved.

Goddamnit

You are now a moderator of /sub/trebuchetmemes.

And mouth and nose

I've never worked construction but it makes sense to me to store the concrete at the highest floor, especially if you will be using it on every floor in the building.

I wouldn't do it to stop people from stealing it, but it seems you could hoist the entire pallet using a crane, and it would then be easier to carry cement bags DOWN the building to where you need it instead of carrying it up if you stored it on the ground.

Not to take away from your effort, but I think this guy that replied below you modeled it more accurately.

I just did this calculation on /sub/holdmybeer and found the force to be equivalent to ~500lbs. I made some very different assumptions though

okay so I have no life and decided to figure out the force required to catch that bag.

Assumptions

dumbass on the roof is holding the bag at 4m (~12ft) Arm level of dumbass_2 is 1m (3ft) Dumbass_2 has roughly a 1/3m (1ft) space to slow the bag to zero m/s (catch it without flipping/dropping) 23kg (50lb) bag of concrete

because this isn't a real problem gravity is 10m/ss. See attached .

First we calculate how fast the bag is going to find the velocity of the bag at time of impact with the arms of dumbass_2 using v22 = v02 +2g(x1). Where x1 = 3m

Next we take the v22 value and plug into v32 = v22 + 2(a2 + g)x2, Where a2 is the deceleration needed to fight gravity and slow the bag and x2 is the 1/3m window to do it in.

From this we get a2 = -100m/s2

Next we calculate the force needed with F=ma. m=23kg and a=-100m/s2

We find that the force needed is 2300N, or the equivalent of holding a 517lb static sack.

Good thinking guys

On a side note, I think it's funny how cement bag keeps getting heavier each repost.

/sub/fullscorpion

I just wanted to shit on some catapults with someone. FUCK CATAPULTS

Do you throw the medicine ball 10 feet in the air and catch it?