What does the term up in arms means?

Angry, rebellious, as in The town was up in arms over the state's plan to allow commercial flights at the air base. This idiom originally referred to an armed rebellion and was so used from the late 1500s.

lets g

the boy's acceleration toward the girl is 2.08 m/s^2.

explanation:

according the newton's third law, the force causing the girl accelerate towards the boy will be me with equal counter-force causing the boy to accelerate towards the girl. these forces will be of equal magnitude and allows us to determine the boy's acceleration:

the boy's acceleration toward the girl is 2.08 m/s^2.