Estimating Car Speed from Skid Marks

  • Thread starter Thread starter nordqvist11
  • Start date Start date
  • Tags Tags
    Car Marks Speed
Click For Summary
SUMMARY

The discussion focuses on estimating the speed of a car from skid marks measuring 92 meters in length, with a constant deceleration of 7.00 m/s². The kinematic equation v² = u² + 2as is utilized to derive the initial speed (u) before braking. The correct interpretation of speed versus velocity is emphasized, clarifying that speed is the magnitude of velocity without direction. The final calculation indicates that the initial speed of the car is approximately 35 m/s.

PREREQUISITES
  • Understanding of kinematic equations, specifically v² = u² + 2as
  • Knowledge of concepts related to acceleration and deceleration
  • Familiarity with the distinction between speed and velocity
  • Basic algebra skills for manipulating equations
NEXT STEPS
  • Review kinematic equations for constant acceleration in physics
  • Practice problems involving speed and velocity to reinforce understanding
  • Explore real-world applications of skid mark analysis in accident reconstruction
  • Learn about the effects of different road conditions on braking distance
USEFUL FOR

This discussion is beneficial for physics students, automotive engineers, and accident reconstruction specialists who need to understand the relationship between skid marks and vehicle speed estimation.

nordqvist11
Messages
15
Reaction score
0

Homework Statement


In coming to a stop a car leaves skid marks 92m long on the highway. Assuming a decceleration of 7.00 m/s^2 , estimate the SPEED of the car just before braking.

I have a question though, is my approach ok? You can see my confusion in various parts of my procedures below, I guess it's the fact that it says find speed not velocity.

Homework Equations


Kinematic Equation for constant acceleration.



The Attempt at a Solution



Physics_2.png
 
Physics news on Phys.org
Speed=velocity lol
 
I got -35m/s as my velocity though
 
Speed is the magnitude of velocity and has no direction.

EDIT: Assuming you are using the formula: v^2=u^2+2as you may need to check what you are using as v and u and be careful of your signs.

0 = u^2 +2as
u^2=-2as

Does that make sense?
 
Last edited:

Similar threads

  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 9 ·
Replies
9
Views
5K
Replies
5
Views
3K
Replies
4
Views
3K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 17 ·
Replies
17
Views
4K
Replies
8
Views
3K
Replies
4
Views
3K