Estimating Car Speed from Skid Marks

  • Thread starter Thread starter nordqvist11
  • Start date Start date
  • Tags Tags
    Car Marks Speed
AI Thread Summary
To estimate the speed of a car that leaves skid marks 92 meters long while decelerating at 7.00 m/s², the kinematic equation v² = u² + 2as can be applied. The confusion arises between speed and velocity, as speed is the magnitude of velocity without direction. The calculation yields a negative value for velocity, indicating a need to reassess the signs used in the equation. By rearranging the formula, the initial speed can be determined correctly. Understanding the distinction between speed and velocity is crucial for accurate calculations.
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:

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Finding speed when given deceleration and distance?
Replies
2
Views
2K
Car Crash Analysis: Analyzing Friction & Speed
Replies
9
Views
4K
Calculating Car Accident Speed: 100ft skid marks, 0.75g deceleration
Replies
5
Views
3K
How Does Kinetic Friction Affect Skid Mark Length and Initial Car Speed?
Replies
4
Views
3K
Was the Driver Speeding Before the Crash?
Replies
9
Views
3K
Solve Physics Problem: Stopping a Car with Skid Marks
Replies
4
Views
2K
Speeds regarding 2D inelastic collision
Replies
8
Views
3K
Speed of train car when sand spilling out from it
Replies
17
Views
4K
Was the Car at Fault Speeding in the Notre-Dame Street Accident?
Replies
8
Views
2K
Calculating Separation of Cars in a Convoy Moving at Max Speed
Replies
4
Views
3K

Hot Threads

Recent Insights

Back
Top