Reaction time of car physics

[JDR 007]

Homework Statement

Determine the stopping distances for a car with an initial speed of 85 km/h and human reaction time of 1.0 s for the following accelerations.
(a) a = -4.0 m/s2
m
(b) a = -8.0 m/s2
m

Homework Equations

d=v1+v2/2 *t
a=change in velocity/time

The Attempt at a Solution

I converted 85kh/h into 23.61m/s
I found how many seconds in each instance
(a) 5.9s...I did -4=(0-23.61)/t solved for t
(b)2.95s...same as a
using these times I used (23.61+0)/2 *Time then added 1 for the reaction delay

I got (a)=82 and (b)=47

What am I doing wrong?

 

[atavistic]

Subtract time.

 

[m2003]

I would first check if the equations and conversions used are correct. The formula for stopping distance, d, is actually d = v0t + 1/2at^2, where v0 is the initial velocity. So for (a), the stopping distance would be (23.61 m/s)(5.9 s) + 1/2(-4.0 m/s^2)(5.9 s)^2 = 69.3 m. For (b), the stopping distance would be (23.61 m/s)(2.95 s) + 1/2(-8.0 m/s^2)(2.95 s)^2 = 34.6 m. These values are significantly different from the ones you calculated.

Additionally, it is important to note that these calculations assume a constant acceleration throughout the entire deceleration process, which may not be the case in real life. Other factors such as friction and air resistance may also affect the stopping distance of a car. Therefore, it is important to conduct experiments and gather data to accurately determine the reaction time of car physics.