Hey there! Sign in to join this conversationNew here? Join for free
Turn on thread page Beta
    • Thread Starter
    Offline

    11
    ReputationRep:
    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    20
    ReputationRep:
    6.5 is obtained using radians instead of degrees. In SHM radians are usually used, but I think in the actual exam they will probably specify.
    Posted on the TSR App. Download from Apple or Google Play
    • Study Helper
    Offline

    21
    ReputationRep:
    Study Helper
    (Original post by assassinjeev22)
    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
    cos10t is written in the form: \text{cos}(\omega t)

    where \omega = 2\pi f

    i.e. 360o = 2\pi radians
    • TSR Support Team
    Offline

    21
    ReputationRep:
    TSR Support Team
    (Original post by assassinjeev22)
    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
    Convention is to work in radians for SHM rather than degrees - this would give 6.48... which rounds off to 6.5mm as required
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by Protostar)
    Convention is to work in radians for SHM rather than degrees - this would give 6.48... which rounds off to 6.5mm as required
    Oh my goodness thank you!
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by Sint)
    6.5 is obtained using radians instead of degrees. In SHM radians are usually used, but I think in the actual exam they will probably specify.
    Awesome thank you!
    • Thread Starter
    Offline

    11
    ReputationRep:
    (Original post by uberteknik)
    cos10t is written in the form: \text{cos}(\omega t)

    where \omega = 2\pi f

    i.e. 360o = 2\pi radians
    Thank you!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: October 12, 2017
Poll
“Yanny” or “Laurel”

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.