As a science project, you drop a watermelon off the top of the Empire State Building, 320 m above the sidewalk. It so happens that Superman flies by at the instant you release the watermelon. Superman is headed straight down with a speed of 36.0 m/s.
How fast is the watermelon going when it passes Superman?

-72.03 m/s (since it's moving down).

Explanation:

To find the speed of the watermelon going when it passes Superman, we need to see both cases, the watermelon and Superman:

For Watermelon:  

   (1)

Where:

y₀ = is the initial height = 320 m

v₀ = is the initial speed = 0 (since it's dropped)  

g = is the gravity = 9.8 m/s²      

t: is the time

For Superman:  

  (2)

Where:

y₀ = is the initial height = 320 m      

v₀ = is the initial speed = -36.0 m/s                

g = is the gravity = 0 (since he's flying at speed constant)  

t: is the time

Since the height, y, is the same for watermelon and Superman when they meet (when the watermelon reaches Superman), we can equal equations (1) and (2):        

 (3)

Solving equation (3) for t, we have:

Hence, the watermelon reaches Superman in 7.35 s.

Now, we can finally find the speed of the watermelon when it passes Superman:

Where:

vf: is the final speed of watermelon (when it passes Superman)

Therefore, the speed of the watermelon when it passes Superman is -72.03 m/s. The minus sign is because the watermelon is moving down.

I hope it helps you!

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it

b. a lightning bug, plug of grass, and a worm