# quest---two particles of mass 1kg n 3kg move towards each other under their mutual force of attraction. no other force acts on dem.tjheir rel...velocity of approach is 2m/s. find vel.of centr of mass/. well mjhe quest galat lag raha tha......wat u thnk.......since its ans is nt given.. so m nt confirm

Aakash Dutta
29 Points
11 years ago

Well I also think that it is incomplete

The initial conditions are not given

Are they at rest?

If yes then

The v of COM remains unchanged = 0

419 Points
11 years ago

Dear Hemant

Question is correct

suppose particles(m and 3m) are placed at some distance r. take origin at m

position of centre of mass= m*0+3m*r/4m = 3r/4 from m

now if they start moving then from action reaction force on both will be same but due to mass difference acceleration will not be same. if acc of m is a then acc of 3m will be a/3. so there will be relative acceleration they will move towards each other with relative acc of 4a/3 and the value of a will not be constant. as gravitational force is proportioal to 1/r2 hence a is also proportional to 1/r2. centre of mass will also change its position as both move with diff acc and diff velocity.

so please confirm the question that is the force constant or v=2m/s is at what instant.

All the best.

AKASH GOYAL

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SAGAR SINGH - IIT DELHI
879 Points
11 years ago

Dear student,

Here concept of reduced mass wll be used..

Mr=m1m1/m1+m2

All the best.

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