Drop something, and stored energy becomes motion energy: $mgh = \tfrac{1}{2}mv^2$. Now watch the $m$ on both sides — it cancels. Solve, and $v = \sqrt{2gh}$ (v equals root two g h): the landing speed does not care what the mass is. Galileo dropped that fact off a tower four centuries ago, and it still lands.

These are two-step problems: bank the energy at the top, cash it at the bottom. Write the middle answer down with its units before moving on — and estimate first. One order-of-magnitude guess costs five seconds and catches almost every slipped root and missing g.