# Homework Help: Position of an oscillating object

1. Nov 9, 2016

### ChloeYip

1. The problem statement, all variables and given/known data

The position of an object that is oscillating on an ideal spring is given by the equation x =
(12.3 cm) cos[(1.26s-1)t]. At time t = 0.815 s,
(a) how fast is the object moving?
(b) what is the magnitude of the acceleration of the object?

2. Relevant equations
As follow
3. The attempt at a solution
dx/dt = -12.3*(1.26)sin(1.26*.815) = -0.2777 cm/s but the answer is -13.3cm/sec
dx^2/dt^2= -12.3*(1.26)^2*cos(1.26*.815) = -19.524 cm/s^2 but the answer is -10.1cm/sec^2

I have only little time before test.hope there is someone help me soon.tell me whats wrong with it.
(Please don't ask me to guess... i m not good at that and i really have not time left...)
Thank you very much for helping me

2. Nov 9, 2016

### vela

Staff Emeritus
$12.3 \ne 1.23$ for one thing.

3. Nov 9, 2016

### ChloeYip

Thanks for reminding
Thats only multiple of 10, still canet get the answer
Also, the calculated answer is not affect by this typo
Sorry for typo

4. Nov 9, 2016

### vela

Staff Emeritus