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1. Aug 5, 2015

nicholas0211510

I'm new to physics I tried doing some research but I can't seem to fully grasp the concept.
My question is, how would one find how much energy is needed to destroy a object a select distence away from the blast

For example if a star when super nova and had a x amount of joules, and let's say a planet was 10 AU away, and that planet was earth and the energy needed to destroy it was 2×10^32 joules

How would you calculate the intensity of the intial explosion to be able to still destroy the planet at that distance?

I believe it was square inversed law but I'm not sure could someone help me out?

2. Aug 6, 2015

Staff: Mentor

Hi nicholas0211510.

If the energy spreads out uniformly in all directions, then imagine a sphere totally enclosing the exploding body. At whatever distance out from the centre of the exploding body you choose to draw the enclosing sphere, all that liberated energy will be spread over the surface of the sphere and you can calculate a Joules/m2 figure for that radius out. Do this calculation for whatever distance away the planet is located, and see whether you can figure out the remaining step.

3. Aug 6, 2015

nicholas0211510

Thank you, I didn't imagin it would be as simple as that

4. Aug 6, 2015

nicholas0211510

I figured you would need to find a lot of variables like I was reading about the square inversed law, but i guess that formula does not associate with the topic at all?

5. Aug 6, 2015

Staff: Mentor

The inverse-square law certainly does apply: if you double the radius of the enclosing sphere, the Joules/m2 changes by a factor of 1/4.

6. Aug 6, 2015

nicholas0211510

I see, I appreciate the help