Answer:
t=20s
Explanation:
To solve this problem we must apply the first law of thermodynamics, which indicates that the energy that enters a system is the same that must come out, resulting in the following equation
For this problem we will assume that the water is in a liquid state, since it is a domestic refrigerator
q=m.cp.(T2-T1)
q=heat
m=mass of water =600g=0.6Kg
cp=
specific heat of water=4186J/kgK
T2=temperature in state 2=20°C
T1=temperature in state 1=0°C
solving:
q=(0.6)(4186)(20-0)=50232J
A refrigerator is a device that allows heat to be removed to an enclosure (Qin), by means of the input of an electrical energy (W) and the heat output (Qout), the coefficient of performance COP, allows to know the ratio between the heat removed ( Qin) and the added electrical power (W), the equation for the COP is
To solve this exercise we must know the value of the heat removed to the water (Qin)
solving for Qin
Qin=(COP)(Win)
Qin=(5)(500W)=2500W
finally we remember that the definition of power is the ratio of work over time
w=work
p=power=500w
When storm clouds produce lightening and thunder, then, potential energy changes into kinectic energy.
The clouds become negatively charged,and the ground is positively charged during a storm. So there creates a potential difference between the charged clouds and the ground. And when this becomes huge so much that it over comes the electrical insulation cover of air, the electrons jump to the ground.i.e. the potential energy changes into kinetic energy.
The first reason is that in the past humans didn't necessarily see the connections between the oceans and thus labelled them that way separating them into 5 oceans and the names stuck to this day.
Secondly, while all the oceans of the world constitute one large Ocean, people need some way to identify each part of it since it is easier to think when we have different categories instead of one large category.
Hope that helped!
C) alternating current .
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B)direct current </span>
Answer:
The average velocity is 40km/h.
Explanation:
The average velocity is 
, where 
is the distance traveled and 
the time elapsed.
The distance traveled is clearly 80km since it's all done in the same direction, we only need to know the time elapsed. For this we calculate the time elapsed on the first part, and add it to the time elapsed on the second part using always the formula 
, where v is the velocity on each part, which is constant.
The time elapsed for the first part is 
, and the time elapsed for the second part is 
, giving us a total time of 
=2h.
Finally, we can calculate the average velocity: 
.
