An object is undergoing shm with period 0.900 s and amplitude 0.320 m. at t = 0 the object is at x = 0.320 m and is instantaneously at rest. calculate the time it takes the object to go (a) from x = 0.320 m to x = 0.160 m and (b) from x = 0.160 m to x = 0.

For an object at Simple Harmonic Motion (SMH), we can write the equation of motion as:
x(t) = A cos[(2 pi/P) t]

where

 P is the period = 0.9

 t is time

A is the amplitude  = 0.32
Therefore for this object we have the equation:
x(t) = 0.32 cos[(2 pi/0.9) t] 

A. Calculate t from x = 0.320 m to x = 0.160 m

We know that at t = 0 the value of x would be: x=0.32 since cos 0 = 1. So we only have to find the value of t when x =0.16m. Using the equation:

0.16 = 0.32 cos[(2 pi/0.9) t] 
0.5 = cos[(2pi/0.9) t] 
pi/3 = (2 pi/0.9)t

t = 0.15 s

 
Therefore it takes 0.15 s to go from 0.32 to 0.16m

B.  Calculate t from x = 0.160 m to x = 0
The time at which x = 0 is: 
0 = 0.32 cos[2 pi/0.90)t] 
pi/2 = (2 pi/0.90)t 
t = 0.225s 

Therefore it takes 0.225s-0.150s = 0.075s to go from 0.16 to 0 m.

the order for strong to weak forces such as

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

the fundamental forces are those forces that act between to objects or element to make interactions. there are four types of fundamental forces such as strong and weak nuclear forces (due to protons and electrons), electromagnetic force (due to the motion of electrons) and gravitational force (due to orbital movement of the planet). if these forces are arranged on the basis of their maximum strength then the order is

strong nuclear force → electromegnetic force → weak nuclear force → gravitational force

3. dark matter

empty space could also be a simple vacuum