Calculating Force Needed to Stop a Moving Vehicle

  • Thread starter Thread starter JPhysic
  • Start date Start date
  • Tags Tags
    Force Vehicle
Click For Summary

Discussion Overview

The discussion revolves around calculating the force required to stop a moving vehicle, specifically focusing on the braking force needed for a car with a curb weight of 1457 kg. Participants explore the relationship between mass, acceleration, and braking force, while also considering factors such as brake disk diameter and the coefficient of friction.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the force needed to stop a car, providing calculations based on speed and mass using the equation F = M x A.
  • Another participant suggests that the coefficient of friction between the brake pads and rotors is necessary for accurate calculations and mentions the need for integration concerning the rotor's radius.
  • Some participants express confusion regarding the initial question, with one clarifying that braking involves torque applied to the wheels rather than a direct linear force.
  • There is a correction regarding the misuse of units, as one participant points out that mass should not be multiplied by speed to derive force.
  • Participants discuss the need for consistent units and the importance of using the correct equations, including work and distance in the context of braking.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to calculating the required braking force, as there are multiple interpretations of the problem and differing opinions on necessary factors and equations.

Contextual Notes

There are unresolved issues regarding the assumptions made about braking dynamics, the role of torque, and the correct application of physics equations in this context.

JPhysic
Messages
8
Reaction score
0

Homework Statement



I am just enquiring about car brakes, and figuring out how much force needs to be applied to stop a moving object (car).


Homework Equations



1457Kg – Curb weight of the car (overall mass)

F = M x A

1457kg x 10mph = 14570 (Newtons)
1457kg x 20mph = 29140 N
1457kg x 30mph = 43710 N
1457kg x 40mph = 58280 N
1457kg x 50mph = 72850 N
1457kg x 60mph = 87420 N
1457kg x 70mph = 101990 N

The Attempt at a Solution



So I've figured out the acceleration, but I need to find out, how much force needs to be applied to bring the car to a stand still using 312 Diameter brake disks. Would it be equal to or greater than the Acceleration?

Thank you for any help you may offer!
 
Physics news on Phys.org
JPhysic said:

Homework Statement



I am just enquiring about car brakes, and figuring out how much force needs to be applied to stop a moving object (car).


Homework Equations



1457Kg – Curb weight of the car (overall mass)

F = M x A

1457kg x 10mph = 14570 (Newtons)
1457kg x 20mph = 29140 N
1457kg x 30mph = 43710 N
1457kg x 40mph = 58280 N
1457kg x 50mph = 72850 N
1457kg x 60mph = 87420 N
1457kg x 70mph = 101990 N

The Attempt at a Solution



So I've figured out the acceleration, but I need to find out, how much force needs to be applied to bring the car to a stand still using 312 Diameter brake disks. Would it be equal to or greater than the Acceleration?

Thank you for any help you may offer!

I believe you will need the coefficient of friction (dynamic) between the brake pads and the rotors. Why would you need that?

And you will probably need to do an integration from the inside to the outside of the swept radius of the rotor, since the braking torque contribution will ratio with the radius.
 
I'm sorry my friend, but you just confused the hell out of me...
 
JPhysic said:
I'm sorry my friend, but you just confused the hell out of me...

Perhaps I misinterpreted your question. I thought you were asking how hard (how much force) you have to squeeze the brake pads together on the rotor in order to brake a car to a standstill. Were you asking something different?

The "brakes" do not apply force directly to a car in a linear fashion. The brake pads sqeezing the rotors apply a braking torque to the wheels, which is what slows the car down...
 
I need to know at:

10mph - 70mph with a mass at 1457Kg, what force is needed to bring the car to a stand still
 
JPhysic said:
I need to know at:

10mph - 70mph with a mass at 1457Kg, what force is needed to bring the car to a stand still

F = M x A

1457kg x 10mph = 14570 (Newtons)
1457kg x 20mph = 29140 N
1457kg x 30mph = 43710 N
1457kg x 40mph = 58280 N
1457kg x 50mph = 72850 N
1457kg x 60mph = 87420 N
1457kg x 70mph = 101990 N

Well, first of all, you don't multiple mass in kg by speed in mph to get force in Newtons.

And you don't multiply mass by speed to get force anyway.

You wrote the equation F=MxA, which is correct. You also need the equation W=FxD (work equals force multiplied by distance). Now, write the equations, and keep your units consistent (use mks units).
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 15 ·
Replies
15
Views
7K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
Replies
4
Views
8K
Replies
2
Views
2K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 1 ·
Replies
1
Views
17K
  • · Replies 2 ·
Replies
2
Views
55K
  • · Replies 4 ·
Replies
4
Views
8K