D, releases a massive amount of energy as heat Hope this helps
<h3><u>Answer;</u></h3>
B. constant acceleration.
<h3><u>Explanation</u>;</h3>
- Free fall is the type of motion of a body or an object when only gravity is acting on it.
- <em><u>All objects undergo free fall on the earth surface at the same rate irrespective of their mass. This is because the gravitational field on the surface of the earth 9.8 N/kg, causes and acceleration equivalent to 9.8 m/s/s of any object in free fall motion.</u></em>
- Therefore,<u> the acceleration of any freely falling object near the surface of the earth is 9.8 m/s².</u>
The common value for “Speed of light in vacuum” is 
metre per second.
Answer: Option b
<u>Solution:
</u>
Speed of light can be defined as the speed with which light waves propagate in different medium. In vacuum, speed of light is 186,282 miles per second or 299,792 km/s which is rounded off as 
.
“Speed of light in vacuum” is a universal constant and usually represented by ‘c’. Light waves travels at a speed of 
metre per second in vacuum.
Answer:
Echoes are the reflection of sound from relatively flat object that is far enough away that you can discern the time difference. Echoes are used to measure distance, velocity, and the shape of objects. Echoes off gratings result in an unusual pinging sound
