Which equation applies to find the displacement of an object that starts from rest?

Correct answer: d s = v²/2a

With u = 0, v² = u² + 2as becomes v² = 2as, so s = v²/2a.

Why the other options are wrong

• a s = at²: s = at² lacks the factor ½. Starting from rest, s = ½at².
• b v = 2as: v = 2as does not balance dimensionally: the right side is m²s⁻² and the left side is ms⁻¹. The correct relation is v² = 2as.
• c s = v/√(2a): s = v/√(2a) puts a square root in the wrong place when making s the subject of v² = 2as. It should be s = v²/2a.