Question 3: What is the net force on a toy locomotive at t=3s?

[LezardValeth]

can someone check my work please thanks, oh btw I am still trying to learn how to use LaTeX mathematical typesetting; I figured itll be slightly faster taking a picture of the problem and my work and posting it here so please bare with me

1. The position of a toy locamotive moving on a straight track along the x-axis is given by the equation x = t^3 - 6t^2 + 9t, where x is in meters and t is in seconds. The net force on the locomotive is equal to 0 when t is equal to (a) zero (b) 2s (c) 3s (d) 4s (e) 5s


(my work)
x = t^3 - 6t^2 + 9t
v = 3t^2 - 12t -- first derivative
a = 6t - 12 -- second derivative
0 = 6t - 12
12 = 6t
t = 2s

Question 2: http://ourworld.cs.com/LezardV4leth/problem_2.jpg
Work: http://ourworld.cs.com/LezardV4leth/problem_2_work.jpg

Question 3: http://ourworld.cs.com/LezardV4leth/problem_3.jpg
Work: http://ourworld.cs.com/LezardV4leth/problem_3_work.jpg

 

[vanesch]

Looks ok to me...

BTW, don't count too much on us to systematically check your homework
We want to help with specific difficulties, misunderstandings or so, but we're not here to do the algebra checks for you

 

[LezardValeth]

oh haha ^^;; Ill make note of that next time thanks a lot though