The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

Physics Simple harmonic oscillations

Im stuck on 4b (iii)
https://www.ocr.org.uk/Images/61757-question-paper-unit-g484-the-newtonian-world.pdf

firstly, im confused on how we know to use the x=Acoswt graph and not x=Asinwt

secondly, where did the 15.5 m come from.

Thanks
You use x = Acoswt when the object begins to oscillate from its max positive amplitude, and the sine version when it begins oscillating from equilibrium.
So when t=0, use the cosine version if it begins from amplitude, and sine for if it begins from equilibrium (think about your sine and cosine graphs).

Im guessing the 15.5m is the average height of the surface of the water. (18+13/ 2) = 15.5m
Hope that helps!
Reply 2
Avatar for fiftythree
fiftythree
OP
12
Original post by Shafi_haque
You use x = Acoswt when the object begins to oscillate from its max positive amplitude, and the sine version when it begins oscillating from equilibrium.
So when t=0, use the cosine version if it begins from amplitude, and sine for if it begins from equilibrium (think about your sine and cosine graphs).

Im guessing the 15.5m is the average height of the surface of the water. (18+13/ 2) = 15.5m
Hope that helps!

Ty for the reply.

What information in the question suggests that the water starts from maximum amplitude
Reply 3
Avatar for fiftythree
fiftythree
OP
12
Can someone help me visualise this
Original post by fiftythree
...

You're right they don't give start position of the tide, cos or sin is fine. Or they assume high tide at t = 0 without stating.

d = 15.5 corresponds to x = 0, the equilibrium of oscillation; d = 18 to x = A, d = 13 to x = -A.

t = 0, high tide: d = 15.5 + x = 15.5 + 2.5cos(wt)
Original post by fiftythree
Im stuck on 4b (iii)
https://www.ocr.org.uk/Images/61757-question-paper-unit-g484-the-newtonian-world.pdf

firstly, im confused on how we know to use the x=Acoswt graph and not x=Asinwt

secondly, where did the 15.5 m come from.

Thanks


For such a question, you can use either Acos(2πft) or Asin(2πft). There is no info within the question that says you must to use Acos(2πft).
Reply 6
Avatar for fiftythree
fiftythree
OP
12
Original post by Physics Enemy
You're right they don't give start position of the tide, cos or sin is fine. Or they assume high tide at t = 0 without stating.

d = 15.5 corresponds to x = 0, the equilibrium of oscillation; d = 18 to x = A, d = 13 to x = -A.

t = 0, high tide: d = 15.5 + x = 15.5 + 2.5cos(wt)

ty

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you