Math Is Fun Forum

paulb203

Member

Registered: 2023-02-24

Posts: 377

Momentum

Object A; 90kg, 2m/s east
Object B; 45kg, 2m/s west

Q. After a collision, if the two objects 'stick' together, and 'become one' (like when a car goes into the back of another car, etc) how do we refer to this new object? Do we call it AB, or something like that?

Q. What is the velocity of this combined object after the collision?

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Prioritise. Persevere. No pain, no gain.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,702

Re: Momentum

What you call it isn't important.  The calculation is

Decide on a positive direction (either will do but then use it throughout).

As the objects are travelling towards each other one v will be + and the other - .

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

paulb203

Member

Registered: 2023-02-24

Posts: 377

Re: Momentum

What you call it isn't important.  The calculation is

Decide on a positive direction (either will do but then use it throughout).

As the objects are travelling towards each other one v will be + and the other - .

Bob

So;

90x2-45x2=(135) x v3

180-90=135 x v3

90 = 135 x v3

v3 = 90/135

v3 = 2/3m/s

And does the calculation mean;

Total p before = Total p after

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Prioritise. Persevere. No pain, no gain.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,702

Re: Momentum

I learnt it as conservation of momentum.  Your calculation is correct.  But should need to add emphasis concerning direction.

So start by declaring you are taking East as the positive direction and end by stating the combined object travels East at 2/3 m/s.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

paulb203

Member

Registered: 2023-02-24

Posts: 377

Re: Momentum

Thanks, Bob.

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Prioritise. Persevere. No pain, no gain.