Asked by peterlaw
A man runs round a circular track at a constant speed.
Would like to know how to drawn locus of the points representing the magnitude ‘d’ of the displacement of the man from the starting position against time ‘t’ , during one lap of the track.
Would like to know how to drawn locus of the points representing the magnitude ‘d’ of the displacement of the man from the starting position against time ‘t’ , during one lap of the track.
Answers
Answered by
Steve
consider the angle θ subtended by the arc he has run on a track of radius r. The location of the point at time t is s*t where s is his speed in units of distance/time.
If we lay out the track so he started at (r,0) and ran in a counterclockwise direction, then at time t, his location is
(x,y) = (r cosθ,r sinθ)
and θ st/r
the distance from (r,0) is thus
d = √((r-x)^2 + y^2)
= r√((1-cosθ)^2 + sin^2θ)
= r√(2-2cosθ)
= 2r sin(θ/2)
= 2r sin(st/2r))
If we lay out the track so he started at (r,0) and ran in a counterclockwise direction, then at time t, his location is
(x,y) = (r cosθ,r sinθ)
and θ st/r
the distance from (r,0) is thus
d = √((r-x)^2 + y^2)
= r√((1-cosθ)^2 + sin^2θ)
= r√(2-2cosθ)
= 2r sin(θ/2)
= 2r sin(st/2r))
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