Physics

Problem

A body moving in a straight line under constant acceleration covers

20\,\text{m}

during the third second of its motion and

30\,\text{m}

during the fifth second. The magnitude of its acceleration is a)

10\,\text{m s}^{-2}

2.5\,\text{m s}^{-2}

5.0\,\text{m s}^{-2}

4.0\,\text{m s}^{-2}

Intuitive explanation

The key is recognizing that distance covered during a specific second means the displacement in that one-second interval, not the total distance from the start. Use the equation for displacement in the $n$ -th second: $s_n = u + \frac{a}{2}(2n-1)$ , where $u$ is initial velocity and $a$ is acceleration. Set up two equations using the third and fifth seconds, then solve for $a$ by elimination—the initial velocity will cancel out, leaving you with acceleration directly.

Intuitive explanation

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