# Why does a car apply a force to a wall?

when we have 0 acceleration(constant speed) like a car travelling at a constant speed,
ƒnet=ma
ƒnet=(mobject+mfriction).(aobject+afriction)
let m object be 1500 kg.
m friction be 10 kg
a object be 0
a friction be 20m/s^2
so when we calculate fnet=-20*1600=-32 000 Newtons.
which means wall applies force towards car but the situation isn't like this.
questions:where did I make a mistake?
2-does friction have a mass or acceleration?

PeroK
Homework Helper
Gold Member
2020 Award
when we have 0 acceleration(constant speed) like a car travelling at a constant speed,
ƒnet=ma
ƒnet=(mobject+mfriction).(aobject+afriction)
let m object be 1500 kg.
m friction be 10 kg
a object be 0
a friction be 20m/s^2
so when we calculate fnet=-20*1600=-32 000 Newtons.
which means wall applies force towards car but the situation isn't like this.
questions:where did I make a mistake?
2-does friction have a mass or acceleration?
This is not good. I guess from your name you are self-learning physics. There are some fundamental problems here. An object has only one mass. The idea of a friction mass is not valid. I can't imagine where you got that idea from.

BvU
Homework Helper
friction have a mass or acceleration?
No. None of the two. Friction is a force.
Dimension mass times length divided by (time squared)
Units kgm/s2

So that is the mistake you make.

In your ##f_{\rm net} = m\, a##
##m## is the mass of the object​
##a## is the acceleration of the object​
##f_ {\rm net} ## is the net force on the object : the vector sum of one or more of the following:​
• gravity
• normal force
• friction
• external force(s)

• PeroK
sophiecentaur
Gold Member
2020 Award
where did I make a mistake
There is problem in that you have not actually stated the situation / problem - except implied in the title.
It's sometimes very hard to get started with this sort of thing and you need to marshal your thoughts if you want to make progress with it.
Does the car hit the wall and come to a standstill?
Do you want to know the Force that acts on the car?
Where do you think friction comes into the collision calculations?
What do you know about collisions and the rules that we apply in calculations about collisions?
A diagram could help, perhaps - either draw one just for yourself or post it.

A.T.
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