Final answer:
To answer the question, one would apply the law of conservation of momentum, as it is a physics problem involving a boy jumping onto a skateboard, which relates to the momentum before and after the jump.
Step-by-step explanation:
The student's question involves a physics concept known as conservation of momentum. To solve the problem of a 35 kg boy running at 4 m/s and jumping on a stationary 5 kg skateboard, one would apply the law of conservation of momentum, which states that the total momentum of a closed system remains constant provided no external forces are applied. The initial momentum of the system is solely due to the boy, as the skateboard is stationary. The boy's momentum is his mass multiplied by his velocity (35 kg × 4 m/s). After the jump, the combined mass of the boy and the skateboard would move with a common velocity, which can be found by equating the initial and final momentum (m1×v1 = [m1+m2]×v2, where m1 is the mass of the boy, v1 is the initial velocity of the boy, m2 is the mass of the skateboard, and v2 is the final shared velocity).