Answer:
<em>The average speed of the train is 45 km/h</em>
Explanation:
<u>Speed</u>
It's defined as the distance (d) per unit of time (t) traveled by an object. The formula is:

Let's call x the total distance covered by the train. It covered d1=1/3x with a speed of v1=25 km/h. The time taken is calculated solving for t:



Now the rest of the distance:
d2 = x - 1/3x = 2/3x
Was covered at v2=75 km/h. Thus the time taken is:



The total time is:



Simplifying:

The average speed is the total distance divided by the total time:

Simplifying:

The average speed of the train is 45 km/h
Answer:
D. Freezing?
Explanation:
Get water, put it in the freezer, turns into ice after a few hours.
Answer:
C.Vacuum
Explanation:
There are three methods of transfer of heat:
1) Conduction: conduction is the transfer of heat by direct contact between the molecules of two objects (or two substances). The particles of the hotter object vibrate faster than the particles of the colder object, so energy is transferred by collisions of the molecules from the hotter object to the colder object.
2) Convection: convection is the transfer of heat by mass movement of molecules. This occurs in fluids (liquids or gases), when an external source of heat is applied to the fluid. As a result, the part of the fluid closer to the source gets warmer, so it becomes less dense and rises, while the colder part sinks and replaces the hotter part, forming a convective current. The process continues until the heat source is removed.
3) Radiation: radiation is the transfer of heat carried by electromagnetic waves. Electromagnetic waves can travel in any medium and in a vacuum, so they are the only type of heat transfer that can occur in a vacuum (while conduction and convection cannot occur in a vacuum).
Answer:

b)

Explanation:
Let the amplitude of SHM is given as A
so the total energy of SHM is given as

now we know that
a)
kinetic energy is given as

here

so now we have


now its fraction with respect to total energy is given as

b)
Potential energy is given as

so we have

so fraction of energy is given as
