Answer
When the person raises his arms upwards, he is applying force to them upwards. By Newton's third law, the arms as well apply force of same magnitude downwards, hence increasing the weight.
Similarly, when he brings the arms down, he is applying force downwards. By Newton's third law, the arms as well apply force upwards, which thus decreases the weight.
Work Step by Step
When the person raises his arms upwards, he is applying force to them upwards. By Newton's third law, the arms as well apply force of same magnitude downwards, hence increasing the weight.
Similarly, when he brings the arms down, he is applying force downwards. By Newton's third law, the arms as well apply force upwards, which thus decreases the weight.
