# Question About Physics Homework (High School Physics)

#### streetracer14

Okay, I have stuck on this question for about 10 minutes now, and just thought I would ask you guys for some help. Okay, the question is "A 2229.5 kg car is coasting along a level road at 31.1 m/s. A constant braking force is applied, such that the car is stopped in a distance of 70.2 M. What is the magnitude of the braking force? Answer in units of N"

Any help would be appreciated!!

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#### Integral

Staff Emeritus
Gold Member
You know the initial speed and the stopping distance. Use that to find the time it takes to stop. Look at your equations of kinematics.

Once you know the time you know the average acceleration.

Can you finish?

#### BishopUser

I'll give you a hint, F = ma

#### DatsunKing

wait we aren't finding acceleration, we're finding deacceleration? right?
lol

does it matter which?

#### BishopUser

deceleration is just a fancy way to say that the acceleration is negative or opposing the velocity, so they should be the same magnitude but you may tack on a different direction depending on which word you use (one word carries an inherent negative)

#### streetracer14

Okay, well I think I got it, but can someone post like a step-by-step on how to do this, because I think I got the answer right, but just not sure how to get there... lol

#### hage567

Homework Helper
Post your steps and we'll tell you if you've got it right.

#### streetracer14

okay, well I just went over them again, and I realized I did some of it wrong and now I am lost. So far, all I did now is take the 70 .2m/31.1m/s and got about 2.24. I'm not sure if this is correct, but what now?!?! I'm getting frustrated with this (not you guys, the problem)

#### hage567

Homework Helper
What are you trying to find there? I would start by finding the acceleration, which you can do by using one kinematic equation. Look at them and pick the one that has the things you know in it, along with acceleration which you want to find.

#### Integral

Staff Emeritus
Gold Member
Show us what you are doing!

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