Posted by Sean on Wednesday, October 13, 2010 at 6:20pm.
A duck has a mass of 2.9 kg. As the duck paddles, a force of 0.07 N acts on it in a direction due east. In addition, the current of the water exerts a force of 0.21 N in a direction of 60° south of east. When these forces begin to act, the velocity of the duck is 0.12 m/s in a direction due east. Find the magnitude and direction (relative to due east) of the displacement that the duck undergoes in 2.7 s while the forces are acting. How do you get the direction?

physics  Henry, Friday, October 15, 2010 at 5:55pm
f = ma,
0.07 = 2.9a,
a = 0.07/2.9 = 0.024 m/s^2,
d1 = Vo*t + 0.5*at^2,
= 0.12*2.7 + 0.5*0.024*(2.7)^2,
= 0.3481 + 0.0880 = 0.4361 m., E.
0.21 = 2.9a,
a = 0.21 / 2.9 = 0.0724 m/s^2,
d2 = 0.12*2.7 + 0.5*0.0724*(2.7)^2,
= 0.3481 + 0.2639 = 0.6120 m.@ 60
deg S. of E. = 300 CCW.
RESULTANT(R)
X = hor = 0.4361 + 0.6120*cos300,
= 0.4361 + 0.306 = 0.7421 m.
Y = ver = 0 + 0.6120*sin300 = 0.530m
tanA = y/x = 0.5300 / 0.7421 = 0.7142
A = 35.5 deg = 35.5 deg S.of E. = 324.5 deg CCW.
R = X + iY = 0.7421  i0.5300
R = X / cosA = 0.7421 / cos324.5 = 0.9115 m @ 35.5 deg. S.of W.
DISPLACEMENT(D)
D = R  Vo*t,
= (0.7421  i0.5300)  0.12*2.7
= 0.7421  0.324  i5300,
= 0.4181  i0.5300,
tanB = Y / X = 0.5300/0.4181=1.268,
B = 51.7 Deg = 308.3 deg CCW.
Magnitude = x / cosB = 0.4181 / cos308.3 = 0.6751 m.
Direction = 51.7 deg S. of E.

physics  alberto, Friday, January 28, 2011 at 7:09pm
there is absolutely no way its that complicated. and at points it looks like you made up some values. be more clear.
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