Find Speed of car based on stopping distance and decceleration.

[aprymek]

1. A car leaves skid marks 85 meters long. It slows down at a rate of 4m/s^2. How fast was the car traveling?
Again, totally confused. Don't know where to start.

 

[hage567]

You must show some attempt at working the problem to receive help. Could you explain what part is confusing you? What kinematic equations do you think would fit the information you are given?

 

[nlightner]

To find the speed of the car, we can use the equation: v^2 = u^2 + 2as, where v is the final velocity, u is the initial velocity, a is the acceleration, and s is the stopping distance.

In this case, we know that the stopping distance (s) is 85 meters and the acceleration (a) is -4m/s^2 (since the car is slowing down). We can rearrange the equation to solve for the initial velocity (u).

u = √(v^2 - 2as)

Plugging in the known values, we get:

u = √(0 - 2(-4)(85))

u = √(0 + 680)

u = √680

u ≈ 26.08 m/s

Therefore, the car was traveling at a speed of approximately 26.08 meters per second before it started slowing down.