Motion problem: motorist's braking time including reaction time

  • #1

Homework Statement



A motorist is travelling at 10m/s in a car whose maximum deceleration rate is 5.0 m/s^2

The effective reaction time between seeing a hazard and starting to brake is 0.5s

  1. Calculate the thinking distance for the drover ar this speed (ie the distance travelled during his reaction time)
  2. Calculate the minimim braking distance (ie the distance travelled during maximum deceleration)
  3. the total minimum stopping distance at 10 m/s
  4. The car approaches traffic lights at 12 m/s and the lights turn red when it is 20m from the line. Show whether it is possible for the car to stop before reaching the line and calculate how far from the line it will stop.

Homework Equations




The Attempt at a Solution


  1. s= 10 x 0.5 = 5m
  2. s= 10 x 2 x 1/2 x (-5) -> s= 10 m
I am stuck on 3. and 4. and dont know where to start
 
Last edited by a moderator:

Answers and Replies

  • #2
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
35,533
6,430
s= 10 x 2 x 1/2 x (-5) -> s= 10 m
10m is right, but I don't understand how you get 10 x 2 x 1/2 x (-5), or how that becomes 10. Looks like -50 to me.
I am stuck on 3.
In part 1 you found the distance travelled before starting to decelerate, and in part 2 the distance while decelerating. Part 3 asks for the total.
 

Related Threads on Motion problem: motorist's braking time including reaction time

  • Last Post
Replies
4
Views
2K
Replies
13
Views
234
  • Last Post
Replies
4
Views
1K
Replies
1
Views
3K
  • Last Post
Replies
5
Views
6K
  • Last Post
Replies
1
Views
4K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
2
Views
4K
Replies
2
Views
7K
  • Last Post
2
Replies
29
Views
984
Top