The instantaneous velocity is how the position is changing with respect to time in a specific point in time, as opposed to the average value given by Delta(x)/Delta(t). It's given by taking a limit of Delta(x)/Delta(t) where t approaches 0, that is, by derivating x(t) in respect to t.
v(t) = x'(t) = (28 + 12.4t + 0.045t^3)' = 12.4 + 0.135t^2
But we want to find the velocity at t = 8s:
v(8) = 12.4 + 0.135*(8)^2 = 21.04m/s
Answer:
D)
Explanation:
The Period-Luminosity relationship tells us that luminosity increases with the period, and of course the more luminosity a star has the more far away they can be seen, so from this we know that:
A) False since lower luminosities can be observed when they are close.
B) False since longer periods means higher luminosities
C) False since lower luminosities can be observed when they are close.
D) True: Variable stars with shorter periods have lower luminosities, so they can only be observed when they are close.
Our sun is quite average when looking at all the stars in the Universe. There are stars that are smaller, like Wolf359, and there are also larger stars, like Betelgeuse. Our sun is essentially right in the middle of the star-size spectrum.
If earth was not tilted on a axis, we wouldn't have any seasons. we wouldn't have seasons because the axis tilts us towards or away from the sun, and if you're tilted torwards the sun the sun you would have summer. if you're tilted away from the sun, you have winter. if there was no axis, the temperature would be the same all around the earth, so therefore we would not have seasons.
hopefully this helps
To minimize loss of heat or absorption of heat from surroundings
