Question

is the momentum conserved when a car hits a wall and comes to a complete stop?

Answer 1

yes it is

Answer 2

what will the equation of conservation of momentum will then be?

Answer 3

can u state the principle of conservation of momentum?

Answer 4

initial p=final p provided no external force acts on system

Answer 5

unless we consider deformation or the infinitesimal motion of wall, the eqn will be mv=0

Answer 6

which is not possible

Answer 7

so... in the car collision with the wall.. what are you considering as ur system?

Answer 8

the car and the wall

Answer 9

ok so when the car bangs into the wall.. are there external forces involved?

Answer 10

not if i consider the car and the wall as a system and ignore air resistance/ friction

Answer 11

another question. in an elastic collision between a moving object and a stationary object, can. is it always true that the obj on the left can only bounce back or stop? (1d motion) why can't it also move in the positive direction too

Answer 12

ignore the 'can'

Answer 13

positive direction is assumed to be right

Answer 14

plz don't mention multiple questions in one thread.. and don't jump to next.. before we finish or come to the conclusion of the first


you think there are no external forces?
The wall is connected to the ground right? so don't u think ground is putting force on the wall which is part of your system?!

Answer 15

the wall along with the wall and the ground/earth as well as the car is within the system

Answer 16

the car*

Answer 17

then you are considering the entire earth and the car as your system :D.. in that case.. the momentum will be conserved !

Answer 18

and the equation is....?

Answer 19

it can't be mv=0, can it?

Answer 20

another example is tomato hitting the ground

Answer 21

the car transfers its momentum to earth.. but earth is so massive, that u can hardly feel the velocity!

Answer 22

so will it be like lim dv->0 mv=Mdv

Answer 23

thank you anyway

Answer 24

can you answer the second question or do u want me to make another thread

Answer 25

no its ok..

if a huge rock comes and bumps into a small pebble.. do u think the rock will change its direction and go back?!