Question

Calculate the tension in a vertical strand of spider web if a spider of mass 8.00×10−5 kg hangs motionless on it.
(b) Calculate the tension in a horizontal strand of spider web if the same spider sits motionless in the middle of it much like the tightrope walker in Figure 4.17. The strand sags at an angle of 12o below the horizontal. Compare this with the tension in the vertical strand (find their ratio).

Answer 1

Assume the web strands have negligible weight.
(Hint: It is helpful to draw a FBD of each of these situations to better understand the forces and angles involved.)

a) vertical forces sum to 0:
Ft - Fg =0
Ft - ( 8.00 * 10^-5 kg )( 9.81 m/s ² ) = 0
Ft = ______ N

b) vertical forces sum to 0:
2Ftsin12 - Fg = 0
2Ftsin12 - ( 8.00 * 10^-5 kg )( 9.81 m/s ² ) = 0
Ft = ______ N

You can likely work out the ratio of these 2 results.