A runners arm swings rhythmically according to the model Yss

A runner\'s arm swings rhythmically according to the model Ys-sin4 where t is time in seconds and y is the angle formed with the vertical position. At what time(s) does the arm form an angle of 0.25 radian? 20.

Solution

Y = 1/3*sin(4pi*t/3)

Now Y = 0.25 radian

Then

0.25 = 1/3*sin(4pi*t/3)

sin(4pi*t/3) = 0.75

4pi*t/3 = arcsin(0.75)

4pi*t/3 = 0.848

t = (3*0.848)/(4pi) = 0.202 sec