HELP! Oscillation Problem Solution

[Kudo Shinichi]

HELP!A problem on oscillation

Homework Statement
the equation of motion of an object is y(t)=2.0cos(0.5t+pi/4)meter
a) Find its maximum acceleration and maximum speed, and its position at the time of these maxima.
b) what is the speed of the object when it is +1.2m from its equilibrium position?
c) what are the kinetic potntial and total energies at that point?


The attempt at a solution
a) for this part I don't reall understand what does the question mean by the maximum, is it when cos equals to 1?
b) derive 2.0cos(0.5t+pi/4), which equals to -2sin(0.5t+pi/4)*0.5=-1sin(0.5t+pi/4)
then plug the 1.2 into the unknown variable, which equals to -sin(0.5*1.2+pi/4)=-0.98 I don't really think it is the correct solution for this part
c) I have to find out the correct v from part B and plug into both kinetic and potential energy equation, but I have one more problem here, which is how do i get mass for this question?
P((1/2mv^2)i) + K(1/2mv^2)i) = P((1/2mv^2)f) + K(1/2mv^2)f)

Thank you for helping me.

 

[LowlyPion]

You're given the equation for motion.

velocity is the first derivative.

acceleration is the second derivative.

At what value of t then do each of these functions reach their max?

 

[Kudo Shinichi]

You're given the equation for motion.

velocity is the first derivative.

acceleration is the second derivative.

At what value of t then do each of these functions reach their max?

Sorry, but i still don't quite understand what does max mean, does it mean that when cos or sin equals to 1?

 

[LowlyPion]

Sorry, but i still don't quite understand what does max mean, does it mean that when cos or sin equals to 1?

I'd say so.