1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Alert driver vs Sleepy Driver distance traveled

  1. Jul 4, 2012 #1
    A car is travelling at 120 km/h (75 mph). When applied the braking system can stop the car with a deceleration rate of 9.0 m/s2. The typical reaction time for an alert driver is 0.50 s versus 2.0 s for a sleepy driver. Assuming a typical car length of 5.0 m, calculate the number of additional car lengths it takes the sleepy driver to stop compared to the alert driver.

    I worked this out first by using v^2=Vo^2 + 2a(Δx) to get the distance traveled
    0= 33.3m/s^2 + (-9m/s^2)(x)
    x= 61.7m

    Then, I used d= vt for driver #1: (33.3m/s)(.5s)= 16.7m
    and for driver #2: (33.3m/s)(2.0s)= 66.7m

    Then, I added 61.7m to each driver's distance:
    driver #1 total dist traveled=78.4m
    driver #2 total dist traveled= 128.4m

    Then, subtract 78.4m from 128.4m to get the total extra distance traveled by the sleepy driver. Then, divide this figure by 5m to get total car lengths additional.

    128.4m- 78.4m = 50m/5m= 10 car lengths.

    Now, after going through the problem it appears my initial step is really unnecessary because I could have just used d=vt for driver #1 and driver #2 and took the difference of those figures divided by 5m to get car lengths extra for the sleepy driver. Am I correct? Unless the question was asking for total distance traveled by both or either driver, then step #1 isn't even needed and this problem could have solved much quicker.

    Please confirm.

    Thanks!
     
  2. jcsd
  3. Jul 4, 2012 #2
    Yes

    d1=vt1 +(v2/2a)

    d2=vt2 +(v2/2a)

    Δd=d2-d1
     
    Last edited: Jul 4, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Alert driver vs Sleepy Driver distance traveled
  1. Driver and Car (Replies: 3)

  2. Driver rod (Replies: 1)

Loading...