But in your previous graph you illustrated that lower launch velocities result in shallower angles of impact?
That’s lower velocities for an object of the same mass. 
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While delightful, I feel Shi-rakansu’s response pipped it:
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But then it would be a question of testing different masses at the same launch velocity, which you can’t do if you fix the initial energy given. I guess the difference between that and B’s graph would be to keep the volume and shape constant instead of the density (so two spheres at different densities for example). I really don’t see how mass makes it steeper.
Well, you don’t necessarily have to test it - you can think about trends. That’s what @Kutsushokunin was trying to get at with the discussion about melons of infinite mass.
Basically, at one end of the scale, your infinite-mass melon will launch with zero velocity, so it’ll land right at your feet, with an angle of 90°. As you reduce the mass, it’ll launch with greater and greater velocity, and so land further away from you, at shallower and shallower angles. Since trends in the real world tend to be smooth and well-behaved, it’s clear, at least from the thought experiment, that the heavier it is, the steeper it hits.
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Right, I just didn’t think the discussion would end at accepting that the distance between the archer’s hands and the ground was included, since that really gives an unfair advantage to objects that make a small arc. Because basically it’s like saying we can disregard everything we discussed about earlier such as mass, initial velocity, and energy, and just say that if we drop it that’s as steep as it gets, and everyone already knew that, it’s nothing insightful.
I just don’t think that there are people here who think heavier objects lead to steeper angles of impact, not including the small distance to the ground of course.
I feel like to real title of this thread is:
Wanikanians do know physics?
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I think the arc of a melon shot from a bow is the least of our worries here.
How do you even intend on firing a melon from a bow ?
(This incidentally illustrates the difference between phycisists and engineers points of interest)
But i think this mostly just comes down to semantics.
If you measure the angle an arrow and a melon, fired with the same energy and inclination, hits the ground. I suspect it will be closer to 90 degrees for a melon than for an arrow. which is probably what the mnemonic creator had in mind. But this certainly does not have much to do with the arc of travel (alright its related but the “steepness” or curvature is another thing).
I see plenty of mnemonics that makes me go “just no”
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You say bow, I say balista. What’s the big deal?
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As an Engineer, I can confirm that physicists do, indeed, assume this quite often. 
It’s the favored food of spherical cows with uniform density.
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The big difference being that the mnemonic is about a bow i suppose 
Potayto potarto
They’re both drawstring.
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ahh yes, a cabin and a castle are the same, they both have walls amirite
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It’s referring to the amount of energy required to fire a melon in a straight line. Arrows fly in a straight line when fired from a bow because they’re light and aerodynamic. A melon is far heavier, and less aerodynamic than an arrow, and heavier, less aerodynamic objects require more energy to move. So wanikani is right here.
Exactly! I’m pleased to see that we’re on the same page in terms of simplification.
My ballista comment was facetious, just to be entirely clear, since a ballista (being essentially a siege crossbow) would be perfect for the job of launching a melon. Of course, there is a lot of presupposition of the melon in question being a watermelon when it may just as well be a sprite or honeydew.
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Time flies like an arrow.
Fruit flies like a banana melon.
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And what about an european one? 
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Using a really big bow. https://www.youtube.com/watch?v=8cfeTZNcA3g
It’s more like a slingshot than a ballista but close enough.
Yeah, I was assuming the start and end point were at the same level. The distance to the ground gives a huge advantage to the melon.
Tell me more about these creatures.
Yeah, we already mentioned the assumption about the distance to the ground giving the melon an advantage.
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Honestly, I’m not even surprised by this. What does WaniKani know and what does it teach you? I’ve certainly never learned anything about paticle physics here!
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I take it that you missed the legendary paticle thread and all the discussion about whether you need lessons to learn them without their kana, then?