Math Is Fun Forum

paulb203

Member

Registered: 2023-02-24

Posts: 429

Physics: Kinetic Energy

True or False:

If an object has zero kinetic energy, it must be at rest.

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Seemed obvious to me at first that it is true as:

K=(1/2)mv^2

and if v=0, then K must =0

But what about reference frames?

A observes a car speeding past and, in A's frame, the driver has  K
B, the passenger in the car, observes the driver next to him in the car, and concludes that the driver has zero K

??

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"The secret of getting ahead is getting started."
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Bob

Administrator

Registered: 2010-06-20

Posts: 10,786

Re: Physics: Kinetic Energy

Good question!  KE must be relative.   When we do the drop from height h  PE = mgh  = KE half mv^2 we don't take account of the Earth moving through space nor its rotation .

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob