Bob who has a mass of 100 kg stands ona. Frictionless frozen lake with a 20 kg rock in his hands. He throws the rock forward with a velocity of +5 m/s. What is the velocity of bob after he throws the rock

Option B

Explanation:

This involves the conservation of momentum:

m1v1 = m2v2

Now initially neither the rock nor Bob is moving. Then the rock moves forward with a velocity of 5 m/s, having a mass of 20 kg. But Bob moves back by the conservation of momentum, so at what velocity?

0 = 20(5) + 100(vf),

-100 = 100vf,

vf = - 1m/s

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