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Why doesn’t a nuclear bomb create a chain reaction that destroys the entire planet?

  Because real life is not Hollywood plus 4 reasons. Fission vs. Fusion : Nuclear bombs work on the principle of nuclear fission – splitting heavy atoms like uranium or plutonium. This releases energy, sure, but to destroy the entire planet? Not enough oomph. What you'd need is a fusion reaction, the kind that fuels stars. That involves lighter atoms like hydrogen fusing, and it's way more powerful. Think of fission as a firecracker, fusion as the sun. We're nowhere near making a fusion bomb as big as our planet. The Limits of Chain Reactions : Even in a fission bomb, the chain reaction doesn't run wild forever. The explosion itself scatters the nuclear fuel, disrupting the critical mass needed to sustain the reaction. It's like trying to keep a bonfire going by throwing the logs across the field. Dissipation of Energy : The colossal energy released by a nuke mostly disperses as heat, light, and a shockwave. Earth is just way too big to absorb all that and go kabloo...
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A car travels at a constant speed of 75 miles per hour. How far in miles will the car travel in 20 minutes?

 Ooh, maths homework eh?

When you’re faced with one of these where it’s two units, just turn the whole thing into the same units. For instance, pounds and pence- just turn the pounds into pence.

This time it’s hours and minutes. So turn hours into minutes. There’s sixty minutes to an hour and so 75/60 = 1.25 (or 1 1/4 if you do it in fractions) miles per minute.

You want to know what it will do in twenty minutes. If it does 1.25 miles in one minute, all you’ve got to do now is multiply by twenty.

20 X 1.25 is 25. Twenty-five miles in twenty minutes.

You could work it backwards too to test your answer. Twenty minutes is a third of an hour. A third of seventy-five is twenty-five. Or to show your working out as they make you do in school:

60 /20 =3 …20 min = 1/3 of an hour.

75/3 = 25…..car travels 25 miles in 20 minutes.

Normally they’re looking to see if you can grasp the idea of finding common units and so the first one is what they’re expecting. On the old O level or CSE the papers would be marked by proper maths teachers who would accept either way but these days they’re often marked by tick-box people and if you don’t follow exactly what’s on their models they might not have the nouse to see that anything else is acceptable. So even though it’s just the same thing they might not realise and you’d lose your working-out marks even though you’ve done it and got the right answer. So go the first way for preference.

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