A mason stretches a string between two points 70 ft apart on the same level with a tension of 20 lb at each end. If the string weighs 0.18 lb, determine the sag h at the middle of the string.

Explanation:

Let tension be T in each string . Let angle with horizontal be θ in the middle

The sum of vertical components of tension of two string will balance the weight

2Tsinθ = mg

2 x 20 sinθ = .18

sinθ = .18 / 40 = .0045

θ = .25783 degree

If sag be y

y / 70 = tan .25783

y = 70 x tan.25783

= .3150 m

= 31.50 cm .

the answer is c. the lower legs are levers, and the knees are fulcrums. the ankles hold the loads.