- #1

baldbrain

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## Homework Statement

To stop a car, first you require a certain reaction time to begin braking; then the car slows down under constant breaking decelaration. Suppose that the total distance moved by the car during these two phases is 56.7 m when its initial speed was 80.5 km/h and 24.4 m when its initial speed 48.3 km/h. What are

(a) The reaction time

(b) Magnitude of decelaration

2. Homework Equations

2. Homework Equations

The Kinematical Equations

## The Attempt at a Solution

Actually, my guess of what they're asking is the time between pressing the brake pedal and the brake pads squeezing in on the tyres.

So let

*t*be the reaction time and

_{o}*a*be the constant breaking decelaration.

u

_{1}= 80.5 km/h = 22.36 m/s

u

_{2}= 48.3 km/h = 13.42 m/s

Now, I thought of using s = ut + (1/2)at

^{2}, get two equations and solve them, but I have one basic question.

In the time interval I think they're asking, the car isn't decelarating. It starts decelarating after the brake pads squeeze in on the tyres. So how can I substitute

*t*&

_{o}*a*in the same equation?