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

Click For Summary

Homework Help Overview

The problem involves a ball of mass 65 g thrown vertically upwards with an initial speed of 16 m/s. Participants are tasked with calculating the ratio of potential energy to kinetic energy at a specific time after the ball is thrown, specifically at time t/2, where t is the time to reach maximum height. The context includes concepts from kinematics and energy conservation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations for time to reach maximum height and the subsequent energy calculations. There are questions about the signs used for acceleration and whether the ball's position should be treated as positive or negative. Some suggest working in symbols to simplify the problem.

Discussion Status

The discussion is ongoing, with various interpretations of the problem being explored. Some participants have offered guidance on recalculating energies and checking assumptions about direction and signs. There is no explicit consensus on the correct approach yet, as multiple interpretations and calculations are being examined.

Contextual Notes

Participants note potential confusion regarding the time variable, with some interpreting t/2 as the time when the ball is back on the ground, which raises questions about the energy states at that moment. There is also mention of the need to clarify the definitions of positive and negative directions in the context of the problem.

  • #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?
 
Physics news on Phys.org
  • #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!
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
5K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
742
  • · Replies 38 ·
2
Replies
38
Views
4K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 5 ·
Replies
5
Views
14K
Replies
6
Views
3K
  • · Replies 9 ·
Replies
9
Views
4K