Register to reply

How do I derive this equation? HELP

by psychfan29
Tags: derive, equation
Share this thread:
Sep13-08, 07:05 PM
P: 9
I started with the equation:
y=yinitial + (vinitialsintheta)t -1/2gt^2

I plugged in t=x/(vinitialcostheta)

to get: y=yinitial + x (tantheta) - [(gx^2)/(2(vinitial^2)(cos^2theta))]

Using derivatives, how do I get from this equation:

y=yinitial + x (tantheta) - [(gx^2)/(2(vinitial^2)(cos^2theta))]

to this equation:


I am completely and totally and utterly confused, bewildered, perplexed, and a list of other things.
Plese help!!!!!
Phys.Org News Partner Science news on
World's largest solar boat on Greek prehistoric mission
Google searches hold key to future market crashes
Mineral magic? Common mineral capable of making and breaking bonds
Sep13-08, 07:31 PM
P: 10
To get from y=yinitial + x (tantheta) - [(gx^2)/(2(vinitial^2)(cos^2theta))]

to this equation:

x(sec^2theta)-[(gx^2(tantheta)(sec^2theta))/(vinitial^2)] ---

Taking y and x not to vary with theta.. then they are taken as constants.
differentiating yinitial wrt theta gets 0,
differentiating x tantheta wrt theta gets x sec^2 theta (differentiate tangent to get sec^2)

You could use quotient rule for the last term to get
[gx^2 . (2 cos theta sin theta)] / [2 vinitial (cos^4 theta)]

before simplifying to get the eventual equation..

Register to reply

Related Discussions
How to Derive an Equation. Introductory Physics Homework 7
Derive Velocity Equation Introductory Physics Homework 3
How would i derive the equation? Introductory Physics Homework 3
Can't Derive Friction From Equation Introductory Physics Homework 9
I have to derive my own equation, I need help General Math 7