We need to find `m` in `v = sqrt((2E)/m)` given that `v=25` and `E = 100,000`.

Substituting:

`25 = sqrt((200000)/m)`

Squaring both sides:

`625 = 200000/m`

Taking reciprocal of both sides:

`1/625 = m/200000`

Multiplying both sides by `200000`, we obtain

`m = 200000/625 = 320\ "kg"`.

Checking our answer in the original equation gives:

`v = sqrt((200000)/320) = 25`. Checks OK!

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