7/31/2019 The Projectile Calculator Solved

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The Question:

From where Kim was standing she could see a bird on the fence that was 3m away. The

fence was 1.4m tall. Jay was standing on the other side of the fence. If Kim was to throw

her CAS calculator over to Jay so he could finish his homework, how far from the fence on

the other side should Jay be standing. We don't want the bird to be hit, or the CAS to get

broken! Explain why and how you come up with the answer you do. This is an exercise in

stating your assumptions. Be clear about what you have assumed and how that affects the

result.

One of the strings of posts in its reply:

My answer is this: Kim decides not to be an idiot by throwing her expensive calculator over

the fence to the fumbling boy on the other side, and instead goes around the stupid fence.

The bird is unharmed.

I came to this answer by being sensible.Student A

Yes this question is not the best when taken literally but what if the fence is on top

of a building with no way around Jay has not done any of his investigations and he

has minutes before it is due what then (and the CAS is Jays after all).

Student B

In the situation you have named, Kim has two options:

1. Throw the thing and most likely damage it or throw it off the building.2. Get Jay, the lazy bugger, to walk up to the wall and pass it over. Even if the

wall is higher, Jay could reach out and grab it as she slid it over the fence.

If she DOES decide to throw it, the equation (assuming the fence rests along

the y axis) would be about y = 0.1x^2 + 2. This was found by a combination of

trial and error (in the case of the 0.1x^2), rational thinking (also in the case of

0.1x^2, as you'd want the CAS to land a little over where Jay is standing so he

could catch it at hand-height) and things we learned in class. Kim has the CAS,

and thus could figure this out herself.

So, she throws it. Unfortunately, she is unable to throw the thing accurately,

and hits the bird. Not only is the bird stunned, but the calculator falls into adirty puddle on the roof of the building. Jay goes to grab it, but the water

makes it slippery and it slips out of his hands and onto the cement beside the

fence. A spark from the friction made by the CAS striking the cement lands on

the fence and sets it alight. The fire quickly spreads to the building's roof. Jay

and Kim panic and scream that they should not have thrown the calculator as

it a very valuable machine and it was very silly to assume that throwing it

over a fence was the best answer.

Both of them failed maths because their maths textbooks were lost in the

blaze that consumed the entire building.

Thus, we have learned that you should not have nice things if you plan to

throw them over fences.

Student A