Conservation of mechanical energy of ball of mass

Click For Summary

Homework Help Overview

The discussion revolves around a problem involving the conservation of mechanical energy for a ball of mass 240 g moving through the air with an initial speed of 20.0 m/s and a gravitational potential energy of 70 J. Participants are exploring how to determine the speed of the ball just before it hits the ground.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between potential energy and kinetic energy, questioning how the initial kinetic energy of the ball at 20.0 m/s fits into the total energy calculation. There is an exploration of the conservation of mechanical energy principle, with some participants suggesting that the total mechanical energy should be considered at different heights.

Discussion Status

The discussion is active, with participants providing insights into the conservation of energy and questioning the initial conditions of the problem. Some guidance has been offered regarding the need to equate initial and final total mechanical energy, but no consensus has been reached on the correct interpretation of the given data.

Contextual Notes

Participants are grappling with the implications of the initial speed and potential energy values, as well as the assumption that total mechanical energy remains constant throughout the motion. There is an acknowledgment that the potential energy at ground level is zero, which influences the calculations being discussed.

checkmarks
Messages
12
Reaction score
0

Homework Statement


A ball of mass 240 g is moving through the air at 20.0m/s with a gravitational potential energy of 70J. With what speed will the ball hit the ground?

Homework Equations


Eg = mgh
Ek = 1/2mv^2
W = mgd

The Attempt at a Solution


this is what i did:
at 0m, potential energy is 0 so kinetic energy must have 70J now.

Ek = 1/2mv^2
70 J = 1/2(0.24kg)v^2
v = 24.15 m/s

I don't know what to do with the 20 m/s that was given and yeah...please help!
 
Physics news on Phys.org
The potential and kinetic energy that it had initially is now all kinetic by the time it reaches the ground.
 
you have

potential energy + kinetic energy = total energy = constant

What is the total energy whe the ball is moving through the air? it's not 70 J.

At a height of 0 m, potential energy is indeed 0, so all the energy must be kinetic.
 
since he total mechanical energy is conserved equate the initial total mechanical energy
(pe+ke)to the final toal mechanical energy.
remeber pe=mgh ,so what is pe at ground level?
 

Similar threads

  • · Replies 21 ·
Replies
21
Views
2K
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 2 ·
Replies
2
Views
5K
Replies
4
Views
1K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 13 ·
Replies
13
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
6K