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Simple harmonic motion question help watch

1. 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!
2. 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.
3. (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:

where

4. (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
5. (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!
6. (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!
7. (Original post by uberteknik)
cos10t is written in the form:

where

Thank you!

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