Question

A car with good tires on a dry road can decelerate at about 5.0 m/s^2 when braking. Suppose a car is initially traveling at 55 mi/h. What is the stopping distance

Answer 1

From the kinematic equation, the distance travelled by the car is the following (see https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/a/what-are-the-kinematic-formulas):

$$\Delta x = \dfrac{v_f^2 - v_i^2}{2a}$$

where $v_f = 0m/s$ is the final speed (car stops at the end), $v_i = 55mi/h \approx 24.59 m/s$ is the initial speed, and $a = -5m/s^2$ is the car's decceleration. Thus, obtain:

$$\Delta x = \dfrac{0^2 - 24.59^2}{-2\cdot 5} \approx 60.47m$$

Answer. 60.47 m.