Dr. Aaron B. answered • 10/11/13

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Silvia S.

asked • 10/10/13a 2kg blob of putty moving at 3 m/s slams into a 2 kg of putty at rest. what is the initial momentum of the two blobs? what must be the final momentum of the two blobs? Also, calculate the velocity of the two stuck together blobs of putty after the collision.

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Dr. Aaron B. answered • 10/11/13

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Charles G. answered • 11/26/13

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Momentum is conserved:

m_{i} v_{i} = m_{f} v_{f}

The initial momentum is 6kg-m/s {2kg X 3m/s}

When the first ball of putty sticks to the second the momentum remains the same {6kg-m/s}, but the mass is now 4 kg. The new velocity would be 1.5 m/s for the 4 kg combined blob.

Brad M. answered • 10/11/13

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Grigori S. answered • 10/10/13

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Kirill Z. answered • 10/10/13

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The initial momentum is **p**=m_{1}**v**_{1}+m_{2}**v**_{2}**, **where by boldfaced letters I denote vector quantities. Since the second blob is at rest, **v**_{2}=0. Then

In the closed system the total momentum is conserved. Therefore, the final momentum is also 6 kg*m/s, directed the same way as the initial momentum. However, since two blobs are now stuck together, the total mass is now M=m_{1}+m_{2}=2+2=4 kg. Therefore,

p=Mv=6=4v; From this v=6/4=1.5 m/s, directed the same way as the initial velocity of the first blob.

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