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

1. Jan 3, 2016

### Marisabel

1. The problem statement, all variables and given/known data
(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 travelled in 1.3 s

2. Relevant equations
x= A cos (wt)

3. The attempt at a solution
The answer must be x= 0.88m

k= 705.6 N/m
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.

2. Jan 3, 2016

### PeroK

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

3. Jan 3, 2016

### Marisabel

yes. I get a different answer.

4. Jan 3, 2016

### PeroK

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

5. Jan 6, 2016

### 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?