<h3>Answer;</h3>
-Temperature
<h3><u>Explanation;</u></h3>
- Sound is a type of mechanical wave, which means it requires a material medium for transmission. It results from the vibration of particles.
- The speed of sound in mediums varies depending on the property of the medium and a number of other factors which includes; temperature, pressure, and humidity.
- Temperature increases the speed of sound wave as particles at higher temperatures tend to possess more energy and thus they will vibrate faster and thus the sound wave will travel faster.
Velocity = displacement/time
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The law of energy conservation states that energy cannot be created or destroyed, so choices B to D are immediately invalid. Choice A can explain this occurrence: <u>A. Some of the energy is used to combat friction, and thus is transformed from mechanical energy to heat.</u>
Answer:

Explanation:
Given data:
Momentum of moving model train, 
Mass of the stationary model train, 
Initial speed of the stationary model train, 
Assume there is no external force is acting on the given train system.
In this case, the total linear momentum of the trains would be conserved.
Let the final linear momentum of the trains be 
Thus,




