A car is traveling at 15 m/s on a horizontal road.The brakes are applied and the car skids to a stop in 4.0 s.The coefficient of kinetic friction between the tires and road is:
A)0.38
B)0.69
C)0.76
D)0.92
E)3.75

Question

Quizplus · Accepted Answer

The coefficient of kinetic friction ($\mu_k$) can be found using the formula $\mu_k = \frac{a}{g}$, where $a$ is the deceleration and $g$ is the acceleration due to gravity (approximately $9.8 \, \text{m/s}^2$). First, we find the deceleration ($a$) using the formula $a = \frac{\Delta v}{\Delta t}$, where $\Delta v = -15 \, \text{m/s}$ (since the car comes to a stop, the change in velocity is -15 m/s) and $\Delta t = 4.0 \, \text{s}$. Thus, $a = \frac{-15 \, \text{m/s}}{4.0 \, \text{s}} = -3.75 \, \text{m/s}^2$. The negative sign indicates deceleration. Then, $\mu_k = \frac{-3.75}{-9.8} \approx 0.38$.

A Car Is Traveling at 15 M/s on a Horizontal