Answer:
Speed
Explanation:
If a vehicle hit any other object then its speed will slow down or some time the vehicle will stop its depends on the force exerted by other object on the vehicle.
The change in speed of vehicle is due to momentum because momentum is always conserved. So to conserve the momentum the speed of the vehicle decreases because after hitting the overall mass is increases.
If the intelligent aliens on that distant planet could receive our signal, and then reply to us INSTANTLY with no delay, then our Scientists on Earth would hear the response <em>eight years after</em> they sent their original greeting.
Light and radio waves both travel through space at the same speed. If our scientists sent a radio transmission to that distant planet, it would take four years for the radio message to get there and be heard. Any response would take four years to travel back to us. If the aliens didn't dilly-dally and sent their response immediately, the round trip would total up to eight years.
This property is called "Opacity".
The question is worded in a difficult way. A more easily understood wording of this question would be:
"<em>What is the name of the property of a material that prevents light passing through?"</em>
That can only be happening if the mass mysteriously increased somehow. I'd like to know how in the world THAT happened.
