Max KE of a squirrel jumping from the top of a tree

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Homework Help Overview

The discussion revolves around calculating the maximum kinetic energy of a squirrel jumping from a height, specifically from the top of a 25 m tall tree, and analyzing the kinetic energy of another squirrel that jumps upward to a height of 4 m before falling back down. The subject area includes concepts of kinetic energy, potential energy, and the conservation of mechanical energy.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss using energy conservation principles and kinematic equations to find the maximum kinetic energy and clarify initial kinetic energy calculations. There are questions about the correct application of formulas and the relationship between initial and final velocities.

Discussion Status

Some participants have provided insights into using energy conservation and kinematic equations, while others express confusion about specific calculations and concepts. There is an ongoing exploration of different methods to approach the problem without reaching a definitive conclusion.

Contextual Notes

Participants are navigating the complexities of combining horizontal and vertical motion, as well as the implications of energy conservation in different scenarios. There is mention of potential misunderstandings regarding terminology, such as the distinction between kinetic and kinematic concepts.

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Homework Statement


1. A squirrel jumps horizontally from the top of a 25 m tall tree with a speed of 8 m/s. What is the maximum kinetic energy of the squirrel during it`s entire trip down to the ground from the top of the tree?
2.If another squirrel of the same mass jumps straight upward from the ground well enough to get 4m off the ground and then falls back to the ground, what is the kinetic energy in the following locations and time:
a)3m above ground, on the way up
b)2m above ground, on the way down
c)1m above ground, on the way down

Homework Equations


Pe:mgh
ke:0.5mv^2
pei+kei=pef+kef

The Attempt at a Solution


I know that we have to use the ke initial and add it with the new kinetic energy that is gained during gthe trip in order to calculate total kinetic energy before it hits the ground for prolem 1. But I am really confused and would appreciate guidance. I do not need the answers just help. :)
 
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Boop de Boop said:
I know that we have to use the ke initial and add it with the new kinetic energy that is gained during gthe trip in order to calculate total kinetic energy before it hits the ground for prolem 1
So where are you stuck, finding the initial KE, finding the KE gained in the fall, or in adding the two?
Can't tell what your confusion is without seeing your attempt.
 
I used the kinematic equation vf^2=vi^2+2ad and found final velocity which is 23.74. Then I plugged into ke-)0.5mv^2. I'm confused with kinetic initial. Is it just ke formula but v final is 8
 
Boop de Boop said:
I used the kinematic equation vf^2=vi^2+2ad and found final velocity which is 23.74. Then I plugged into ke-)0.5mv^2. I'm confused with kinetic initial. Is it just ke formula but v final is 8
That kinetic equation is usually used for one dimensional motion, but here the initial velocity and the acceleration are in different directions.
However, it will give the right result here thanks to Pythagoras; see the later Edit below. Suppose we take that equation and multiply it everywhere by ½m:
½mvf2=½mvi2+mad, where d is the height of the descent and a is g. You can see that this represents
Final KE = initial KE + lost GPE.
I.e. it is the equation for conservation of mechanical work.

Edit: if you want to do it by kinetics rather than work conservation, a more usual path would be to treat the horizontal and vertical separately:
vfx2=vix2+0 (no horizontal acceleration)
vfy2=viy2+2(-d)(-g), where viy=0.
Then you can add these to get the square of the landing speed.
 
Last edited:
Boop de Boop said:
A squirrel jumps horizontally from the top of a 25 m tall tree with a speed of 8 m/s. What is the maximum kinetic energy of the squirrel during it`s entire trip down to the ground from the top of the tree?
From energy conservation KEheight+mgh=KEground+0 where KEground is the max. KE
 
Boop de Boop said:
2.If another squirrel of the same mass jumps straight upward from the ground well enough to get 4m off the ground and then falls back to the ground, what is the kinetic energy in the following locations and time:
From energy conservation
KEi+0=KEheight+mgh ,
During upward journey.
During downward journey
mghmax=mgh+KEheight
 
Apashanka said:
From energy conservation KEheight+mgh=KEground+0 where KEground is the max. KE
@Boop de Boop seems to understand that (see post #1), but became confused when trying to solve it with SUVAT equations (see post #3).
By the way @Boop de Boop, you meant "kinetic", not "kinematic". Kinematics concerns the geometry of moving systems. See e.g. https://en.m.wikipedia.org/wiki/Kinematics.
 

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