C. Here\'s how two different students approached pan A. Elizabeth: Since the lit

Question

C. Here's how two different students approached pan A. Elizabeth: Since the little brother is half as heavy as her sister, he must sit twice as far from the pivot in order to ''compensate'' for his lower weight-6 feet instead of 3 feet . Jill: I used the formula for torque, r = Fr, where F is force and r is distance from the pivot. Here, the relevant forces acting on the see-saw are gravitational, the weights of the children: F1 = 60 pounds and F2 = 30 pounds. The big sister sits r1 = 3 feet from the pivot, and we're solving for r2. The torques must balance: F1r1 = F2r2. I plugged in the numbers to get (60 pounds)x(3 feet) = (30 pounds)x r2, and solved for r2 to get 6 feet. The two students got the same answer. Did one (or both) of them get lucky, or are both kinds of reasoning valid? Explain. Are Jill and Elizabeth's reasoning fundamentally the same, fundamentally different, or a mix of those two extremes? Explain.

Explanation / Answer

1) both of them got lucky as the forces acting in this case are perpendicular so reason given by her fits right ,

as torque=RXF so , T= R*F*SIN(THETA)

both of them havent considerd the sin(theta) factor

2) both of the reasons are fundamentally incorrect, hence can be considered fundamentally same

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