Question

a little girl is pulling her sled behind her across the snow. she stops to adjust her hat. the sled keeps moving and hits the girl on the back of the legs. law 1 law 2 law 3

Explanation:

Newton's First Law of Motion (Law 1) states that an object in motion will stay in motion unless acted upon by an external force. In this case, the sled was in motion when the girl was pulling it. When she stopped (an external force on herself), the sled, due to its inertia (tendency to keep moving as per Law 1), continued moving and hit her. There is no calculation of forces ($F = ma$ which is Law 2) or action - reaction pairs (Law 3) relevant here as the key concept is the sled's continued motion due to lack of an immediate external force to stop it.

Answer:

Law 1