Question

A car is being driven along a road at 25 m s-1 when the driver suddenly notices that there is a fallen tree blocking the road 65 m ahead. The driver immediately applies the brakes giving the car a constant acceleration of -5 m s-2.  How far in front of the tree does the car come to rest? Ans: 2.5 m before.

Answer 1

Explanations & Calculations

• Since the deceleration is uniform, apply $\small v^2=u^2 +2as$ and say it comes to stop some $\small x$ meters before,

$\qquad\qquad \begin{aligned} \small 0&=\small (25\,ms^{-1})^2+2(-5ms^{-2})(65-x)\\ \small x&=\small 2.5\,m \end{aligned}$