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Center of mass and velocity problem

  • Thread starter kbyws37
  • Start date
  • #1
67
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If a particle of mass 5.30 kg is moving east at 10.0 m/s and a particle of mass 18.0 kg is moving west at 10.0 m/s, what is the velocity of the center of mass of the pair?


I used the equation
Vcm = P/M
Vcm = [(5.70)(10) + (15)(10)] / [(5.70)+(15)]
Vcm = 10 ms

however, it says that is not the correct answer.
I don't understand why. can someone help?
thanks
 

Answers and Replies

  • #2
165
1
kbyws37 said:
If a particle of mass 5.30 kg is moving east at 10.0 m/s and a particle of mass 18.0 kg is moving west at 10.0 m/s, what is the velocity of the center of mass of the pair?


I used the equation
Vcm = P/M
Vcm = [(5.70)(10) + (15)(10)] / [(5.70)+(15)]
Vcm = 10 ms

however, it says that is not the correct answer.
I don't understand why. can someone help?
thanks
Re-write your equation with units. Does everything work out? Are you putting the right numbers in the right places? It's hard to tell without units. Are all your signs correct?
 
  • #3
67
0
Vcm = P/M where P is (mass kg)(velocity m/s) and where M is the total mass (kg)

Vcm = [(5.70kg)(10m/s) + (15kg)(10m/s)] / [(5.70kg)+(15kg)]
Vcm = 10 m/s

I'm still getting it wrong.
 
  • #4
radou
Homework Helper
3,115
6
You seem to have put 5.7 kg instead of 5.3 kg and 15 kg instead of 18 kg.
 

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