Upward Projectile Motion (Which equation do I use?)

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SUMMARY

The discussion focuses on determining the appropriate equations for calculating the range of upward projectiles in physics. Two methods are highlighted: the range equation and a derivation method. The textbook states a displacement of 40m based on a launch speed of 20 m/s, while the user calculated a displacement of 123m. The conversation emphasizes that both methods are valid under certain conditions, and the choice of method depends on the specifics of the problem, including whether the projectile is launched from an inclined plane.

PREREQUISITES
  • Understanding of kinematic equations for projectile motion
  • Familiarity with the concept of range in physics
  • Knowledge of initial velocity and its impact on projectile trajectory
  • Ability to derive equations from fundamental principles of motion
NEXT STEPS
  • Study the derivation of the range equation for projectile motion
  • Learn about projectile motion on inclined planes and the corresponding equations
  • Review kinematic equations and their applications in different scenarios
  • Practice problems involving varying initial velocities and their effects on range
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and projectile motion, as well as educators looking for clarification on teaching methods for these concepts.

A-linav

Homework Statement


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Homework Equations


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The Attempt at a Solution


This is just for (a) as I have not attempted the others yet. Okay so my question is: How do I know which method/equation to use when finding the range of upward projectiles? Does it matter? I seem to have gotten the same answer (Dh= 123m) for both methods but my textbook didn't explain when to use which equation.
As well... Is my answer even correct? The answer in the textbook says the displacement is 40m but I don't know where they are getting this number.

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A-linav said:
How do I know which method/equation to use when finding the range of upward projectiles?
Both are valid. The "range" equation you used in method 2 is proved using method 1.

A-linav said:
my textbook didn't explain when to use which equation.
As long as the conditions for the range equation are met, you can use it. It gets more complicated when you want the range on an inclined plane, but again, there is an equation you can learn for that.
I was never very confident learning equations, but I could always remember how to derive them.
In the present case, method 1 answers part b as a side benefit.
A-linav said:
The answer in the textbook says the displacement is 40m
The textbook has used 20 m/s as the launch speed.
This is a clear example of a question that has been sloppily modified. In part c, the football has turned into a javelin.
 
haruspex said:
Both are valid. The "range" equation you used in method 2 is proved using method 1.As long as the conditions for the range equation are met, you can use it. It gets more complicated when you want the range on an inclined plane, but again, there is an equation you can learn for that.
I was never very confident learning equations, but I could always remember how to derive them.
In the present case, method 1 answers part b as a side benefit.

The textbook has used 20 m/s as the launch speed.
This is a clear example of a question that has been sloppily modified. In part c, the football has turned into a javelin.

Thanks for your help and for your quick reply! I guess it just depends what is given in the question then :)
 

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