Question

Kyle is driving his car at 15 m/s when he noticed that he is approaching a stalled truck that is approximately 35m away . He steps on the brakes and the car stops 1.0 m away from the stalled truck . At what rate did the car slow down ? Assume that Kyle's reaction time is 2.0s . Reaction time is the time for a person to notice , think and act in response to a given situation .

Answer 1

Explanations & Calculations

• The car travels a total distance of 34m before it comes to a stop.
• The car travels $\small d = 15ms^{-1}\times2.0s=30m$ before the brakes are applied.
• The distance it travels with brakes applied is $\small s = 34 -30 =4 m$.
• u is available, s is available and final speed v is available at the car stops.
• Then using $\small v^2=u^2+2as$, you can calculate the rate.

$\qquad\qquad \begin{aligned} \small 0^2&=\small 15^2+2\times a\times 4\\ \small a&=\small \bold{28.1\,ms^{-2}} \end{aligned}$