The motion of the mass starting from its highest point t=1.3

[Marisabel]

Homework Statement

(a) A large spring has one end attached to the floor and a platform attached to its upper end. On the platform is placed a mass of 30 kg. The mass of the platform itself is 10kg. The spring-platform-mass system is then set into vertical oscillations with a period of 1.5 s. Determine

(i) the stiffness (spring constant) of the spring
(ii) the amplitude of the motion if the maximum speed of the mass is 1 ms-1.
(b) (i) If the motion of the mass (in part (a)) is timed starting from its highest point, calculate how far it has traveled in 1.3 s

Homework Equations

x= A cos (wt)

The Attempt at a Solution

The answer must be x= 0.88m

I've solved part a) already
k= 705.6 N/m
w= 4.2 rad/s
A= 0.24 m

but I'm struggling in part b)
Can someone help me using the formula
x= A cos (wt)PS: This is a past exam paper, I'm using it to study and practice for my exam.

 

[PeroK]

Homework Statement

(a) A large spring has one end attached to the floor and a platform attached to its upper end. On the platform is placed a mass of 30 kg. The mass of the platform itself is 10kg. The spring-platform-mass system is then set into vertical oscillations with a period of 1.5 s. Determine

(i) the stiffness (spring constant) of the spring
(ii) the amplitude of the motion if the maximum speed of the mass is 1 ms-1.
(b) (i) If the motion of the mass (in part (a)) is timed starting from its highest point, calculate how far it has traveled in 1.3 s

Homework Equations

x= A cos (wt)

The Attempt at a Solution

The answer must be x= 0.88m

I've solved part a) already
k= 705.6 N/m
w= 4.2 rad/s
A= 0.24 m

but I'm struggling in part b)
Can someone help me using the formula
x= A cos (wt)PS: This is a past exam paper, I'm using it to study and practice for my exam.

Did you think about plugging $t = 1.3s$ into that equation?

 

[Marisabel]

Did you think about plugging $t = 1.3s$ into that equation?

yes. I get a different answer.

 

[PeroK]

Try plugging in $t = 0s$ and $t=1.5s$ and see if that gives you any ideas.

 

[ehild]

What is x at t=0? And what is x at t=1.3 s? What is the displacement during that time?
By the way, have you set the calculator to radians?