Question

A 1500 kg car decelerates from an initial velocity of 19 m/s to a skidding stop. If the coefficient of kinetic friction is 0.100, how long are the skid marks?

Answer 1

Answer:

19.4 seconds

Explanation:

We have:

m: mass of the car = 1500 kg

v₀: is the initial speed = 19 m/s    

$v_{f}$: is the final speed = 0 (it stops)

$\mu_{k}$: is the coefficient of kinetic friction = 0.100

First, we need to find the acceleration by using the second Newton's law:

$\Epsilon F = ma$              

$-\mu_{k}N = ma$

$-\mu_{k}mg = ma$

Solving for a:

$a = -\mu_{k}g = -0.1*9.81 m/s^{2} = -0.981 m/s^{2}$

Now we can find the time until it stops:

$v_{f} = v_{0} + at$

Solving for t:

$t = \frac{v_{f} - v_{0}}{a} = \frac{-(19 m/s)}{-0.981 m/s^{2})} = 19.4 s$

 

Therefore, the time until it stops is 19.4 seconds.

I hope it helps you!