Question

The Arecibo Observatory sent a powerful radio signal to space in 1974. Assume there is an alien civilization located on a planet around Alpha Centauri (distance 4.2 light-years from Earth) and they detect this transmission. They immediately send an invasion force that travels at 10% of the speed of light. What year ON EARTH will the alien invasion force arrive

Answer 1

1999

Step-by-step explanation:

First of all, it is necessary to calculate the time in which the signal sent by the Observatory arrived to the the planet of the aliens. The time is 4.2 years. That is, the signal arrived in 1978 with 73 days:

`4years+0.2years=4years+0.2(365days)/(1year)=4years+73days`

Now, we have to calculate the time that the aliens take to arrive to EARTH from the planet of aliens (by taking into account that the velocity is 0.2c):

`t=(d)/(c)=(4.2)/(0.2)\approx 21 years`

Hence, the allien invasion will be in the year:

year 1978 + 21 years = 1999

in the year of 1999

hope this helps!!

Answer 2

Answer:

The invasion will arrive in the year 2020

Step-by-step explanation:

Detailed explanation and calculation is shown in the image below