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an elastic ball hits a wall and rebounds with same velocity, what is its change in momentum????? [pls tell me which velocty has to be taken as negative- intial or final and why??? pls explain...}

an elastic ball hits a wall and rebounds with same velocity, what is its change in momentum?????


[pls tell me which velocty has to be taken as negative- intial or final and why??? pls explain...}

Grade:9

4 Answers

Sudheesh Singanamalla
114 Points
10 years ago

Dear shivam ,

there are some conventions to be noted :

1. If a body travels in the positive 'x' direction , it is taken as positive

2. If a body travels in the negative 'x' direction , it is taken as negative

the same is the case with velocity.

here the answer will differ according to the figure drawn.

consider this figure

1843_16302_reflection.jpg

initial momentum = P1 = mv

final momentum after hitting the wall =P2 = m (-v) = -mv

change in momentum = P2-P1 = -mv - mv = -2mv

therefore magnitude of change in momentum = 2mv

 

Please approve

vishal bhatnagar
14 Points
10 years ago

first you have to choose your coordinate axis and then work according to your convention.

vikas askiitian expert
509 Points
10 years ago

consider a ball is moving along +ve x axis & a wall is placed in yz plane...

 

initial velocity = v = u (i)                          (i is unit vector along +x axis)

intial momentam = mv = pi = mv (i)     ..................1

 

now when ball hits the wall it rebounds & its velocity gets reversed ..

final velocity = u (-i)

final momentam = mv (-i)          ....................2

change in momentam = initial - final momentam

                             = mu (i) - mu (-i)

                            = 2mu (i)

iit jee
44 Points
10 years ago

hi,

if the mass of ball is m and initial velocity =v

then change in momentum is 2mv!!!!!!!!!!!!!!!

final velocity must be taken negetive!!!!!!!!!!!!!!

 

 

kedar joshi

 

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