Calculating Elastic Force and Projectile Motion: Energy/Work Questions

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Homework Help Overview

The discussion revolves around calculating the elastic force and analyzing projectile motion in the context of a slingshot launching a marble. The problem involves concepts of work, energy, and forces acting on the marble during its ascent.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between work, energy, and force, questioning which height to use in calculations. They discuss the equations for work and energy, and some participants attempt to apply these equations to find the average force exerted by the elastic.

Discussion Status

There is an active exploration of the problem with various approaches being discussed. Some participants provide guidance on the equations to use, while others express uncertainty about the correct application of these equations. Multiple interpretations of the problem are being considered.

Contextual Notes

Participants are navigating the constraints of the problem, such as the specific heights to consider and the definitions of work and energy in this context. There is a focus on ensuring the correct application of physics principles without reaching a definitive conclusion.

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Homework Statement


An elastic powered slingshot can launch a 100 g marble into the air 18 m by using elastics.
a) W hat is the average force exerted by the elastic if the elastics stretches 65.0 cm before it launches the
marble?
b) How fast is the marble going straight up when it is 10 m above the ground?
c) W hat speed does the marble leave the sling shot?
d) How high is the marble from the ground when it is moving at 10 m/s?

Thanks!

Homework Equations

The Attempt at a Solution


So i know W=Eg=mgh, but what height would i put for h? 18m or 65 cm?
 
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Madeline1844 said:

Homework Statement


An elastic powered slingshot can launch a 100 g marble into the air 18 m by using elastics.
a) W hat is the average force exerted by the elastic if the elastics stretches 65.0 cm before it launches the
marble?
b) How fast is the marble going straight up when it is 10 m above the ground?
c) W hat speed does the marble leave the sling shot?
d) How high is the marble from the ground when it is moving at 10 m/s?

Thanks!

Homework Equations

The Attempt at a Solution


So i know W=Eg=mgh, but what height would i put for h? 18m or 65 cm?

Welcome to the PF.

a) What is the equation for Work as a function of Force and Distance? Given your W=mgh equation, what is the energy that the marble has when it leaves the launcher?

b) What is the equation for Total Energy in terms of Potential Energy and Kinetic Energy?

c) (combine a & b...)

d) (similar to b)
 
which height has gravity being the only Force applied?
. . . how do you compute Work from Force?
 
so (.1)(9.8) (.65) should give me energy/work which i can then rearrange to find force?
 
Madeline1844 said:
so (.1)(9.8) (.65) should give me energy/work which i can then rearrange to find force?

Not quite. What equation are you trying to use there? What are the units of each quantity? It's a good idea to get in the habit of first writing the equation symbolically and then writing it with numbers and units for each symbol, and then etc... :smile:
 
I tried using W=Eg=mgh.
(0.1)(9.8)(0.65)
that would give me 0.637 as the p.g.e/work so then i could put it into W=Fd and solve for f
0.637=F(0.65)
0.98N=F
 

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