Originally Posted by

**elliotyang** Dear Knowledge,

I think your approach is kind of long winded.

For this case, F=-kx=mg

it is obviously seen that g and k are constant when compare the two situation since g is 9.81m/s^2 while k=spring constant. (since using the same spring, this vqlue should be the same for both)

So from this, we can deduce that m is directly proportional to x.

use this relation would be much faster.

instead you plug in the value into the formula compute, and then reverse it. of course it is not wrong, just kind of wasting time.