Answer:
U₂ = 400 KJ
Explanation:
Given that
Initial energy of the tank ,U₁= 800 KJ
Heat loses by fluid ,Q= - 500 KJ
Work done on the fluid ,W= - 100 KJ
Sign -
1.Heat rejected by system - negative
2.Heat gain by system - Positive
3.Work done by system = Positive
4.Work done on the system-Negative
Lets take final internal energy =U₂
We know that
Q= U₂ - U₁ + W
-500 = U₂ - 800 - 100
U₂ = -500 +900 KJ
U₂ = 400 KJ
Therefore the final internal energy = 400 KJ
Answer:
y = 17,89 m
Explanation:
Let us fixate the reference point in top of the building, from where the watermelon is thrown down. We will assume also that the positive axis of our system points up. We describe the watermelon’s motion with the equation:

Clearing the equation so we isolate y we have that:

Making a substitution with the values from the statement we have:
]
So, this skyscraper is about 17,89 m tall; which is not very tall for a skyscraper but who am I to judge. 17,89 m is also the displacement of the watermelon from the point it was thrown down.
I hope everything was clear with my explanation. If I can help with anything else, just let me know. Have an awesome day :D