Question

How much joules of energy is released from a 40mm grenade blast?

and another question? at what velocity would a jeep (2.150tonnes) lets say its initialy stationary, be projected from this explosion if the grenade was to hit the road just next to it, not actually hitting the vehicle itself?

Answers

James is correct. To know the answer to this question you would need to following information:

- Mass of explosive in the grenade you are talking about (and thus the number of moles of explosive).

- The type of explosive and its associated enthalpy of formation/decomposition/detonation (no doubt will be a very exothermic reaction so will be negative meaning release of energy if you're interested).

However! A lot of explosives have an energy rating done a on a per mass basis and it just so happens that TNT has an energy concentration of 7.5MJ/kg (wikipedia). That's 7 500 000J per kilogram of TNT explosive. So, let's say that your grenade has 50 grams of TNT in it (I don't know if these are realistic numbers but for arguments sake I needed to put a figure on it).

Energy capacity = 50/1000 x 7 500 000 = 375kJ of stored energy in the hypothetical 50gram TNT grenade.

So what does this mean? well, you might be saying "there's more energy in a candy bar" and you'd be quite right, there is. Only difference is the time in which the energy is released. A grenade explosion is an instantaneous release of energy so this is 375kJ instantly released to the surroundings. Would it tip over a jeep? No. The energy to tip over a jeep would be very large as you are dealing with a large mass (force required to accelerate a mass is given by Force=mass x acceleration). Also it is complex question in that the energy from the grenade doesn't all go into tipping the jeep over. The explosion intensity may obey the inverse-square law, I'm not sure. Anyway, point is, only some of the energy will be successfully used up in moving the jeep and as 375kJ isn't enough to do it in the first place, it wont be tipping over.

Hopefully that's given you enough insight to investigate further.

#1

A 40mm grenade will not move a jeep. It would rock it slightly, and the shrapnel would put holes in it, but that's about it. You'd need a much larger explosive like an artillery shell to actually displace a vehicle.

You can figure out the energy released in the explosion by estimating the amount of composition B, C-4, or TNT in the grenade and using the detonation enthalpy (delta h det) of the explosive. Remember that C-4 is flammable and its "regular" delta-h applies only to slow reactions. I'm guessing the h-det will be smaller; explosions are much more impressive than fires, but they are very brief compared to fires.

#2

Purely depends on how it is hit. explosives are designed to explode things, unfortunately. Some sort of pressure explosion might do it. Can't sugest much without knowing more.

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#3