Answer:
y₀ = 10.625 m
Explanation:
For this exercise we will use the kinematic relations, where the upward direction is positive.
y = y₀ + v₀ t - ½ g t²
in the exercise they indicate the initial velocity v₀ = 8 m / s.
when the rock reaches the ground its height is zero
0 = y₀ + v₀ t - ½ g t²
y₀i = -v₀ t + ½ g t²
let's calculate
y₀ = - 8 2.5 + ½ 9.8 2.5²
y₀ = 10.625 m
Before you start working on any motion problem, YOU decide which direction you're going to call 'positive'. Everybody almost always calls UP positive, and the acceleration of gravity points down, so it winds up negative. But you could just as well call DOWN the positive direction. Then, the cannonball is fired with a negative vertical speed, and the acceleration of gravity eventually robs all of its negative speed, and makes it start falling in the positive direction. The whole thing is your choice.
It uses electromagnetic radiation waves to enable military communications, navigation, radar, nonintrusive inspection of aircraft, and other equipment. Hope this helps.
More cool stars produce much of their light in the red part of the spectrum, so you see them, and bam, the color red. More hot stars, however, produce much more of their light in the green and or yellow spectrums, with much more tinier amounts of red / blue. This balance of the colors, your eye, sees simply as white. The more hot something is, the greater frequency of radiation it produces! Blue light has a higher frequency than red light, so the stars that glow red are cooler, than the stars that glow blue. :)
Hope this helped!
