Textbkpg36

__Text book page 36 # 14-16__ 14) A different scaffold that weighs 300 N supports two painters, one 250 N and the other 300 N. The reading on the left scale is 400 N. What is the reading on the right scale? Ans: Use equilibrium rule: Summation of Forces =0 ∴ (x+400) - (250+300+300) = 0 x = 850 - 400 x = 450 N

15) Nellie Newton hangs at rest from the ends of the rop as shown. How does the reading on the scale compare to her weight? Ans: Since Nellie is at rest: Summation of Forces = 0 ∴ Reading of the scale = Nellie's weight

16) Harry the painter swings year after year from his bosun's chair. His weight is 500 N and the rope, unknown to him, has a breaking point of 300 N. Why doesn't the rope break when he is supported as shown at the left? One day Harry is painting near a flagpole, and, for a change, he ties the free end of the rope to the flagpole instead of to his chair as shown at the right. Why did Harry end up taking his vacation early? Ans: ∵In the first case, Summation of Forces =0 F1 + F2 = 500 N If F1 = F2, F1 = F2 = 250 N < 300 N ∴ The rope won't break But in the second case, F1 = F2 = tension on the rope = 500N > 300 N ∴ The rope is broken, therefore the painter falls down and hurt.