A piston rises to 5 cm and falls to 3 cm in such a way that it returns to the maximal height three times every two seconds. If we start observing the piston at its maximal height, find an equation modelling the height, h, t seconds from the initial observation.

(1 cm)cos3πt

Step-by-step explanation:

Since the piston starts at its maximal height and returns to its maximal height three times evert 2 seconds, it is modelled by a cosine functions, since a cosine function starts at its maximum point. So, its height h = Acos2πft

where A = amplitude of the oscillation and f = frequency of oscillation and t = time of propagation of oscillation.

Now, since the piston rises in such a way that it returns to the maximal height three times every two seconds, its frequency, f = number of oscillations/time taken for oscillation where number of oscillations = 3 and time taken for oscillations  = 2 s

So, f = 3/2 s =1.5 /s = 1.5 Hz

Also, since the the piston moves between 3 cm and 5 cm, the distance between its maximum displacement(crest) of 5 cm and minimum displacement(trough) of 3 cm is H = 5 cm - 3 cm = 2 cm. So its amplitude, A = H/2 = 2 cm/2 = 1 cm

h = Acos2πft

= (1 cm)cos2π(1.5Hz)t

= (1 cm)cos3πt