Deceleration of Car before Barrier – Rankers Physics

Equations of Motion: Practice Problem & Solution

A car is travelling at \(72\text{ kmh}^{-1}\) and is \(20\text{ m}\) from a barrier when the driver puts on the brakes. The car hits the barrier 2s later. What is the magnitude of the constant deceleration?
\(7.2\text{ ms}^{-2}\)
\(10\text{ ms}^{-2}\)
\(36\text{ ms}^{-2}\)
\(15\text{ ms}^{-2}\)

Solution Explained:

To solve this problem, we apply the core principles of Equations of Motion. Understanding the underlying formula is key to arriving at the correct answer below:

Initial velocity \(u = 72\text{ km/h} = 20\text{ m/s}\). Using \(s = ut - \frac{1}{2}at^2\): \(20 = 20(2) - \frac{1}{2}a(2)^2 ⇒ 20 = 40 - 2a ⇒a = 10\text{ ms}^{-2}\).

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