A duck waddles 2.5 m east and 6.0 m north. What are the magnitude and direction of the duck's displacement with respect to its original position?

1 Answer
May 27, 2017

Magnitude: #6.5 "m"#
Direction: #67^o# north of east

Explanation:

We'll label the positive #x#-axis east (to the right), and the positive #y#-axis north (upward).

To find the magnitude of this displacement, we can use the formula

#r = sqrt(x^2 + y^2)#

where #r# is the magnitude of the displacement vector,
#x# is how far along the #x#-axis it was displaced, (how far east or west it is) and
#y# is how far along the #y#-axis it was displaced (how far north or south it is).

This equation is essentially the distance formula, but with the starting position at the origin.

It traveled #2.5 "m"# east, so we'll substitute #2.5 "m"# for the #x# value, and it traveled #6.0 "m"# north, so we'll substitute #6.0 "m"# for the #y# value. This gives the magnitude of the displacement

#r = sqrt((2.5"m")^2 + (6.0"m")^2) = color(red)(6.5 "m"#

The direction of the displacement vector is found according to the equation

#tantheta = y/x#

And so the angle, #theta#, of the displacement vector (with respect to the positive #x#-axis) is

#theta = arctan(y/x) = arctan((6.0"m")/(2.5"m")) = color(blue)(67^o#

(The function #arctan# is the same as the function #tan^-1#, which you're more likely to see on a calculator.)

The displacement vector of this motion is thus #6.5 "m"#, #67^o# north of east (counterclockwise from the positive #x#-axis, which is most often where angles are measured from).