I need to plot a projectile motion graph...I am confused..my numbers don't work at all.
The equations I have are the one for the dx component and the dy component. I did the dx values with this equation
dx=(vcostheta)(time)
the dy should be this: dy=(vsintheta)(time)+(1/2a)(time)^2 but when I do this...the numbers don't get bigger then smaller...just bigger! How the heck do you graph this ?
8 answers
What you call dx and dy are probably d wth x and y subscripts. They are not the differential small changes used in calculus. What you have are equations for the x and y coordinates of an object fired wth velocity v and and angle of theta with the horizon. There is a gravitational field actng in the y direction. Your number "a" for the acceleration should be -9.8 m/s^2, the acceleration of gravity. Note the minues sign. The value of dy will not always get bigger. Eventually the object hits the ground.
Yes, you are right the letters x & y are subscripts...so bascially, I have calculated the dx components properly...but should I make up the positive direction and then use the negative acceleration? I tried doing that a way we did in class by making down positive, and then the v in (vcostheta) was negative...that did nothing to my answer but made me have negative values...if I make the acceleration negative will that make a difference?
If you make v postive and a negative, as I suggested, the object will start off going up (increasing dy) and then will come back down.
I don't fully understand, but I sort of do..ha. I made up the positive direction so that the equation became this:
delta dy=(vsinthetat)(time)+(-1/2 9.81)(time)^2
this equation worked well and I had a proper projectile graph! :)
delta dy=(vsinthetat)(time)+(-1/2 9.81)(time)^2
this equation worked well and I had a proper projectile graph! :)
As well, when you are labelling the axis, Delta d x is the horizontal displacement and delta dy is the vertical displacement or both in metres for the units? Or whatever unit is given? Since it is displacement? Thanks, I really appreciate this!
The units of displacement depend on the units of time, velocity, and acceleration. Meters is standard, and standard SI.
Thats what I thought, so the question is in meters, and everything else has meters in it as well, so are the axis labelled with (m)....as well if I have to graph something falling of a cliff..how do I manipulate the equations to do so...
dx=(v1x * time) dy=(1/2 a * Time^2)
dx=(v1x * time) dy=(1/2 a * Time^2)
Ya so honestly...I cant figure out how to graph this graph. OK so Willy throws a coin from the top of a cliff. If he throws it with an initial velocity of 22 m.s in the horizontal direction, plot the trajectory of the coin at intervals of 0.10s. How can this be done? Please help me, the more I look at these questions, the more I wonder why in the world did I take this class? Thanks so much for being smart and taking the time to assist me..you are all helping me out more than you even know!
1 answer