Final answer:
In a see-saw scenario with Barbie in the air and Ken on the ground, Ken should move away from the center to increase the torque on his side and bring Barbie down. So the correcct option is D) move away from the center.
Step-by-step explanation:
The question involves a scenario where Barbie sits on one end of a see-saw and Ken on the other, with Barbie being lifted into the air while Ken remains on the ground. To make Barbie move down, Ken should move away from the center of the see-saw. This concept relates to the principles of torque and levers, specifically the seesaw a type of lever where the fulcrum (pivot point) is in the center.
Since we are told that there is only 1.50 m of board on the side opposite to where Ken is sitting (the seesaw is 3.0 m long), and Ken is currently off the board, for him to exert a downward force effectively, he needs to utilize leverage by moving further from the fulcrum. This increases the torque (rotational force) on his side of the seesaw due to the longer moment arm (distance from the pivot), thus allowing him to counteract Barbie's weight and bring her down.
It's important to know how balancing on a seesaw works: if one child is heavier, they sit closer to the pivot to achieve balance, as the pivot supports the weight of both children. Therefore, to make Barbie go down, the correct answer is D) move away from the center.