What does a 50 lb rock do to a stone building from 500' up?

[Gilladian]

My PCs want to drop large boulders on an ancient evil temple from about 500' in the air (they have a flying device that can hover and give them a very stable platform to drop things from). They're considering bathing the temple with fireballs to heat-stress it first...

This is an E6 campaign, so even though the temple was built by ancient, very powerful and very evil entities, it isn't indestructible. I have no objection to them being able to damage the temple, maybe even punch holes in the roof (it is built solidly of white granite carved into a massive dome-shape, and covered with weird tentacles and such. Real Cthulhuoid appearance...).

I'm thinking that 10-12 such rocks should do the job, which will shatter the integrity of the wards on the temple, meaning that the guardian monster will stop appearing every 15 minutes to defend it, and maybe prevent some other wicked effects inside from working on them... but still not negate ALL the temple's defenses.

Is that reasonable? Any other ideas/suggestions?

(for those with access, this is the temple on the Island of Khorant, on the DungeonaDay site.)

 

[sr123]

If one rock fails to dent or crack or rumble the foundations of the dome, then ten won't make a difference.

A drop that far will have your rocks impacting at about 50 meters/sec. However, 50lbs isn't very heavy, and the dome will be built strong enough to support multiple maintenance workers standing on top. The important thing then is to cause enough vibration in the structure to crumble the mortar or rocks themselves. As long as the rocks hit the dome relatively head-on (not at an angle), and assuming the granite is not reinforced with wood or metal, multiple rocks can be used to get enough vibration that may collapse the roof altogether.

If it is reinforced, however, your only chance is if a single rock can dent or crack it.

 

[Tonguez]

you'll fill it with holes but not knock it down unless you hit an architectural weak point

 

[Gilladian]

But do you think that filling it with holes would be enough to disrupt the wards that summon the guardian monster? Or perhaps other evil effects that are ongoing? I would like them to get SOME advantage for what they've done, but not completely negate the challenges of the temple.

 

[Tonguez]

yep, if that fits the story then yes the wards will be broken

 

[Umbran]

Your typical 12-pound cannonball can have a muzzle velocity of over 1000 feet per second.

A rock dropped from 500' up will have a velocity of about 176 feet per second when it reaches the ground.

While your rocks are heavier, they're moving much more slowly. And since kinetic energy (1/2 * m * v^2) goes with the square of the velocity, I would expect your rocks to be less dangerous than a cannonball.

Your projectile is moving more at trebuchet speeds. But a typical trebuchet projectile was from 2 to 5 times more massive than the rocks you're describing.

So, I'd say this - if the building were designed to take fire from siege engines, then those rocks aren't going to be enough to damage it much. If the building were not so designed, while the walls may stand (because dropping a rock onto the top edge of a stone wall doesn't hurt the wall much) that roof will probably be heavily damaged or destroyed given some effort by the party.

Anyone in the party have skill with engineering will probably know this off the top of their head.

 

[SethDrebitko]

I'd throw the players a bone maybe say that the wards are temporarily dampened by the magical and physical assault, but that they need to move quickly to seize the opportunity. This gives them something in return for the creative idea even though it probably wouldn't have been able to structurally harm the temple.

 

[Janx]

Your typical 12-pound cannonball can have a muzzle velocity of over 1000 feet per second.

A rock dropped from 500' up will have a velocity of about 176 feet per second when it reaches the ground.

While your rocks are heavier, they're moving much more slowly. And since kinetic energy (1/2 * m * v^2) goes with the square of the velocity, I would expect your rocks to be less dangerous than a cannonball.

Your projectile is moving more at trebuchet speeds. But a typical trebuchet projectile was from 2 to 5 times more massive than the rocks you're describing.

So, I'd say this - if the building were designed to take fire from siege engines, then those rocks aren't going to be enough to damage it much. If the building were not so designed, while the walls may stand (because dropping a rock onto the top edge of a stone wall doesn't hurt the wall much) that roof will probably be heavily damaged or destroyed given some effort by the party.

Anyone in the party have skill with engineering will probably know this off the top of their head.

yeah. science.

To clarify: Is the building built to look pretty, or is it built to withstand assault/siege? If the latter, it's probably been attacked before, and don't look pretty, even if it held. Thus, pretty=vulnerable. ugly=sturdy.

It's also worth considering that them saying 50 pound rocks is because they think that's a lot of weight as non-engineers. If a PC has engineering skill, or simple trial and error, they'll know it may not cut it, and then they'll just up the ante with larger rocks.

 

[Umbran]

It's also worth considering that them saying 50 pound rocks is because they think that's a lot of weight as non-engineers.

Also note - in the OP, you mention 10 to a dozen such rocks. That's 500+ pounds - the weight of a couple of people. How much can the flyer carry?

 

[Gilladian]

The flyer can carry around 10 people. It's big! But they have limited ability to dig up and hoist rocks; they have lots of rope but no shovels or picks, so only what they find on an ancient volcanic mountain face.


The temple is sturdier than pretty, but was damaged slightly in a recent earthquake.