[مونتاندا]

ر“A 40-kg skateboarder on a 3-kg board is training with three 5-kg weights. Beginning from rest, she throws the weights horizontally one at a time from her board. The velocity of each weight is 7 m/s relative to her and the board after it is thrown. How fast is she propelled in the opposite direction after throwing the third weight? Assume that the board rolls without friction.”