Determining speed of an object with only a meter stick?

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Homework Help Overview

The discussion revolves around determining the speed of a rock launched by a slingshot using only a meter stick, a rock, and the slingshot itself. Participants explore the implications of measuring speed without direct time measurement, raising questions about the feasibility of the task.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the necessity of measuring time to calculate speed, with some suggesting that using the meter stick to measure distance traveled could provide insights. There are questions about the angle of launch and whether it can be determined with the given materials.

Discussion Status

The discussion is active, with participants offering various perspectives on how to approach the problem. Some suggest that dropping the rock from a height could provide a way to measure distance and time indirectly, while others express skepticism about the constraints of the problem.

Contextual Notes

Participants note the limitation of using only a meter stick, rock, and slingshot, which raises questions about the assumptions made regarding the setup and measurements. There is also mention of gravity as a constant affecting the time of fall, indicating a consideration of physical principles in the discussion.

fattydq
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A child wishes to determine the speed a slingshot imparts to a rock. How can this be done using only a meter stick, a rock, and the slingshot?



This question seems impossible to me, since you would HAVE to take time into account at some point, in some way, to figure out speed, right? So is this a trick question or am I missing something?
 
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Think ballistics. :)

I'll help you get started:
[tex]y(x)=tan{\theta}\cdot x-\frac{g}{2v_0^2cos^2{\theta}}\cdot x^2[/tex]

Where [tex]\theta[/tex] is the angle the initial velocity of the projectile makes with the horizon.
 
Yes, but figuring out the angle would require more than just the meter stick, rock, and sling shot, wouldn't it?
 
fattydq said:
Yes, but figuring out the angle would require more than just the meter stick, rock, and sling shot, wouldn't it?

I don't know about you, but I'm pretty good at making a 45° angle. :P
 
Haha, yeah, that's what's throwing me about this problem though...the fact that you can ONLY use those materials. That's why I think it may be a trick question or something haha.
 
fattydq said:
Haha, yeah, that's what's throwing me about this problem though...the fact that you can ONLY use those materials. That's why I think it may be a trick question or something haha.

I don't think it's a trick question. If you drop the rock from one meter above the ground then the distance traveled by the rock will be zero. Shooting the rock horizontally from the one meter height with the slingshot will send the rock a certain distance before it hits the ground. The higher the speed of the rock, the further it will go, which can be measured with the yard stick.

You then figure out the time, based on how long it takes a rock to fall from one meter height.
Since speed is just distance over time, you'll have your answer.
 
And that time would just be a constant right? The constant of gravity, that is?
 
fattydq said:
And that time would just be a constant right?
In the context of this problem, yes.
The constant of gravity, that is?
Gravity is a constant, but dropping something from a two meter height will yield a different time constant.
 

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