Question

a car is moving at a constant velocity of 20 m/s when the driver hits the brakes because she sees and animal run across the street in front of the car. if the car experiences an acceleration of -2.5 m/s² and the driver brakes for 2 seconds before taking her foot off the brake pedal how fast will the car be moving after braking?
a 15 m/s
b 17.5 m/s
c 22.5 m/s
d 25 m/s

Explanation:

Step1: Recall the kinematic equation

The kinematic equation for final velocity \( v \) is \( v = u + at \), where \( u \) is the initial velocity, \( a \) is the acceleration, and \( t \) is the time.
Here, \( u = 20 \, \text{m/s} \), \( a = - 2.5 \, \text{m/s}^2 \), and \( t = 2 \, \text{s} \).

Step2: Substitute the values into the equation

Substitute the given values into \( v = u + at \):
\( v = 20 + (-2.5)\times2 \)
First, calculate \( (-2.5)\times2=-5 \)
Then, \( v = 20 - 5 = 15 \, \text{m/s} \)

Answer:

A. 15 m/s