What is the velocity of an electron at t = 1.22 s, given its position function?

[ncr7]

This should be a really easy problem but for some reason I keep getting the wrong answers.

The position of an electron is given by = 3.56t - 8.10t2 + 2.53, with t in seconds and in meters. At t = 1.22 s, what are (a) the x-component, (b) the y-component, (c) the magnitude, and (d) the angle relative to the positive direction of the x axis, of the electron's velocity ?

a) I got the answer to be 3.56 m/s
b) I thought was -8.10 m/s^2 but for some reason it is wrong or atleast this online homework is telling me it is
c) I used the magnitude function to find it for the time being 1.22s
sqrt(4.34^2 + (12.056)^2 + (2.53)^2) and I get 13.06m but it also tells me I am wrong with that.
d) then I can't find this out because I have the magnitude wrong. But if I did have it right I would have it to be arcCos(3.56/magnitude) right?

any help would be great thanks :)

 

[ncr7]

figured out part b and c as I got to the end of the problem I saw they wanted it in velocity so I had to take the derivative of r and then solve for x and y values.

I am still having trouble with d though...

 

[ncr7]

I figured it out it ended up being a negative value because my y-component is negative which would make the magnitude of the vectors in the negative direction, and that gives me -79.79.