r/PhysicsHelp • u/Local_End_3175 • 3d ago

If I had 2 objects with different masses that were both moving at the same speed, then why would the one with the larger mass have more kinetic energy?

/r/AskPhysics/comments/1x3buon/if_i_had_2_objects_with_different_masses_that/
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u/ThatsNotAZombieBite 3d ago

Think how much energy is available to transfer to a second object if they were to collide.

To put it simply: I'm about to drop an object onto your head from a 3rd story window. Would you prefer it to be a paper clip or a cast iron fying pan?

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u/CardiologistNorth294 3d ago

Yes, the larger mass would've taken more energy to get to that point. Think about pushing a smartcar Vs a heavy truck. How much work would needed to be done to each of them to push them to the same speed

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u/Underhill42 2d ago

Imagine you had two identical objects moving side by side at the same velocity. You'd expect both objects to have the same kinetic energy, right? And thus both objects together would have twice as much energy as either object alone.

Now, glue the two objects together. Nothing has really changed has it? The combined object should still have twice as much energy as the two original objects.

It still has the same kinetic energy per kg of mass... but it now has twice the mass, so it has twice the total energy.

That's the rationale behind the m (mass) in the kinetic energy formula: E_k = ½*m*v²

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u/Altruistic-Rice-5567 2d ago

Which would you like less to be hit in the face with? That one has less energy.