Calculating Final Speed of a Thrown Object with Changing Momentum

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The discussion centers on calculating the final speed of a 60kg person throwing two 10kg blocks at 5m/s. The initial calculations yield a final speed of 1.67 m/s after throwing both blocks sequentially. However, the correct final speed is 1.55 m/s, which accounts for the changing momentum of the person as she throws each block. The discrepancy arises from the need to consider the relative speed of the blocks with respect to the ground, not just the person.

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A 60kg person is holding two 10kg blocks and she throws them one at a time at 5m/s.
What is her final speed?

What I get is,
after she throws the first rock 0=70v-50 so her speed is 5/7 m/s,
and after she throws the second 5/7 *70=60v-50 so her final speed is 5/3 m/s (1.67 m/s)

But the answer says 1.55 m/s which is less than the speed she would gain if she throws the two rocks simultaneously (5/3 m/s).
What am I doing wrong?
 
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The speed of each thrown block is 5 m/s with respect to the person. As the person's speed changes, so does the speed of a thrown block with respect to the ground.
 
Doc Al said:
The speed of each thrown block is 5 m/s with respect to the person. As the person's speed changes, so does the speed of a thrown block with respect to the ground.

Ofcourse... thank you!
 

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