Answer:
Time use of cellphone times 3 hours before sleep.
Explanation:
It is scientifically proven that cell-phone use before bed can disturb your sleep. The blue light can cause your brain to release chemicals that associate with staying awake or even waking up. So measure the hours or minutes you use your phone 3 hours before you go to sleep.
Answer:

Explanation:
Given that,
The spring constant of spring 1, 
The motion of the object on spring 1 has twice the amplitude as the motion of the object on spring 2, 
As the magnitude of the maximum velocity is the same in each case, it means the maximum kinetic energy is same in each case. In other words, the total energy is same.




So, the spring constant of spring 2 is 920 N/m. Hence, this is the required solution.
Answer:
At 400 m the potential energy of the mountain climber doubled the initial value.
Explanation:
Given;
initial height of the mountain climber = 200 m
final height of the mountain climber, = 400 m
The potential energy of the mountain climber is calculated as;
Potential energy, P.E = mgh
At 200 m, P.E₁ = mg x 200 = 200mg
At 400 m, P.E₂ = mg x 400 = 400mg
Then, at 400 m, P.E₂ = 2 x 200mg = 2 x P.E₁
Therefore, at 400 m the potential energy of the mountain climber doubled the initial value.
Answer:
a) a = 5.03x10¹³ m/s²
b) 
Explanation:
a) The acceleration of the positron can be found as follows:
(1)
Also,
(2)
By entering equation (1) into (2), we have:

<u>Where:</u>
F: is the electric force
m: is the particle's mass = 9.1x10⁻³¹ kg
q: is the charge of the positron = 1.6x10⁻¹⁹ C
E: is the electric field = 286 N/C
b) The positron's speed can be calculated using the following equation:

<u>Where</u>:
: is the final speed =?
: is the initial speed =0
t: is the time = 8.70x10⁻⁹ s

I hope it helps you!