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Homework Statement
A 0.35 kg particle moves in an xy plane according to x(t) = - 11 + 1 t - 6 t3 and y(t) = 19 + 3 t - 8 t2, with x and y in meters and t in seconds. At t = 0.7 s, what are (a) the magnitude and (b) the angle (within (-180°, 180°] interval relative to the positive direction of the x axis) of the net force on the particle, and (c) what is the angle of the particle's direction of travel?
Homework Equations
Fx=m(ax)
Fy=m(ay)
The Attempt at a Solution
I got the first part right by taking the second derivative of each plane and applying it to the equations.
(ax)= dvx/dt = -36t m/s^2
(ay) = dvy/dt = -16 m/s^2
and by applying the relevant equations
Fx= -8.82
Fy= -5.6
By using Pythagoras theorem I found that the net force to be
Fnet= 10.448
Which is right.
After drawing a picture
in part b my attempt to solve was
tan^-1(theta)= Fy/Fx
Which is tan^-1(theta) = -5.6/-8.82
theta = 32.41
which I got wrong
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Part C
My attempt was applying in the velocity functions of both planes which are
Vx= 1-18t^2
Vy= 3-16t
and finding that
Vx= -7.82
Vy= -8.2
After that
tan^-1(theta)= -8.2/-7.82
theta= 46.358
which I also got wrong.Thanks in advance.