Originally Posted by

**ticbol** **c) the first 3 times when the weight is 53cm above floor.**

53 = 10*cos[(2pi/3)(t -0.3) +50

53 -50 = 10*cos[(2pi/3)(t -0.3)]

cos[(2pi/3)(t -0.3)] = 3/10 = 0.3 --------------positive cosine***

angle [(2pi/3)(t -0.3)] = arccos(0.3)

(2pi/3)(t -0.3) = 1.266103673

t -0.3 = 1.266103673 / (2pi/3)

t -0.3 = 0.60452

t = 0.60452 +0.3

t = 0.90452 sec --------------the first time.

Since cosine is periodic, and the period of this particular cosine curve is found at 3sec/cycle, then every 3sec after 0.90452sec, the weight is 53cm above the floor, so,

0.90452 +3 = 3.90452 sec --------------the second time.

3.90452 +3 = 6.90452 sec -------------the 3rd time.