A Ball Is Thrown Vertically Upwards, Find The Ratio of PE to KE

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SUMMARY

The discussion centers on calculating the ratio of potential energy (PE) to kinetic energy (KE) for a ball of mass 65 g thrown vertically upwards at a speed of 16 m/s. The correct ratio is established as 3:1, contrary to initial calculations that suggested 1:1. Key equations used include GPE = mgh and KE = 1/2 mv^2, with the gravitational acceleration (g) taken as -9.81 m/s² to maintain consistency in direction. The importance of working symbolically until the final steps is emphasized to avoid arithmetic errors.

PREREQUISITES
  • Understanding of gravitational potential energy (GPE) and kinetic energy (KE)
  • Familiarity with the equations of motion (SUVAT equations)
  • Basic knowledge of algebra and symbolic manipulation
  • Concept of directionality in physics (positive vs. negative acceleration)
NEXT STEPS
  • Study the derivation of the equations for gravitational potential energy and kinetic energy
  • Learn about the SUVAT equations and their applications in projectile motion
  • Explore the significance of sign conventions in physics calculations
  • Practice solving similar problems using symbolic methods to enhance understanding
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and energy concepts, as well as educators looking for examples of common calculation pitfalls in energy ratio problems.

  • #31
haruspex said:
William, I know you are keen to be very helpful to the posters, and no doubt they are grateful, but the way the homework forums work is that we do not post complete solutions (unless the poster has already found one). We ask questions, provide hints, point out mistakes. In the long term, we believe this is of greater benefit.
yes, I totally understand, but OP was lost after a week of help; and the help was getting more an more abstract.

One piece of helpful advice was "Note that the answer is independent of g, m and u and, in fact, there was no need for any numerical calculations"

Which, is totally useless for somebody that is lost. Why is the answer independent? Why is there no need for calcs? There was no explanation. That was just left there, hanging. Fine if you are au fait with projectile motion - utterly bewildering if you are not. If the OP was already lost, this "smart" help help just made them even more lost!

Surely there is a point where somebody needs to be shown how to do something so they can move forwards? I know that is certainly true for me - especially after a week of frustration trying to figure something out! Isn't that what teachers do?
 
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  • #32
William White said:
yes, I totally understand, but OP was lost after a week of help; and the help was getting more an more abstract.

One piece of helpful advice was "Note that the answer is independent of g, m and u and, in fact, there was no need for any numerical calculations"

Which, is totally useless for somebody that is lost. Why is the answer independent? Why is there no need for calcs? There was no explanation. That was just left there, hanging. Fine if you are au fait with projectile motion - utterly bewildering if you are not. If the OP was already lost, this "smart" help help just made them even more lost!

Surely there is a point where somebody needs to be shown how to do something so they can move forwards? I know that is certainly true for me - especially after a week of frustration trying to figure something out! Isn't that what teachers do?

@William White I can't say I'm happy with this unsolicited abuse. If you're unhappy with what someone else has said to you, then leave me it of, mate!
 

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