Finding Velocity with Kinetic Energy.

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Homework Help Overview

The problem involves a toy rocket's motion under the influence of thrust and gravity, specifically using energy conservation principles to determine its velocity at a certain height. The subject area includes concepts of kinetic energy, gravitational potential energy, and work-energy principles.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to calculate the rocket's acceleration and velocity using kinematic equations, but is reminded to apply energy conservation principles instead. Some participants discuss the work done by the thrust force and its relation to kinetic energy, while others emphasize the need to consider gravitational effects.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of how to apply the work-energy principle. There is a recognition of the need to account for gravitational forces in the calculations, indicating a productive direction in the conversation.

Contextual Notes

Participants are navigating the constraints of using energy conservation rather than kinematic equations, and there is a focus on the definitions and calculations related to work and energy in the context of the problem.

kencamarador
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Homework Statement



I have to use energy conservation to solve this. So i cannot solve with kinematics

"On a windless day, the engine of a 250 g toy rocket exerts 30N of thrust straight upward until it burns out at a height of 165 m"

How fast is the rocket moving at 165m?

Homework Equations



Ek=mv^2 / 2
Em=eg+ek
Eg=mgh


The Attempt at a Solution



First i found my acceleration.

A= f/m
A= (30- 9.8 x .25) / 0.25
=110.2

Then subbed into

Vf^2 = 0 + 2(110.2)x165
190.1

But my teacher told us to use the law of conservation...
 
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Well the work done in moving the rocket 165 m will be equal to the kinetic energy of the rocket at 165 m.

How would you find the work done by the force of 30 N in moving 165 m?
 
rock.freak667 said:
Well the work done in moving the rocket 165 m will be equal to the kinetic energy of the rocket at 165 m.

How would you find the work done by the force of 30 N in moving 165 m?

Mutliply 30 by 165 which is 4950

oh... Then solve for v
 
You need to take into account gravity.
 

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