qu_is (qu_is) wrote in gcsesciencehelp,
qu_is
qu_is
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Physics help??

hey,
I'm doing my Australian HSC physics by distance education. unable to get hold of my teacher for daaaays.
if any one can tell me what I'm doing wrong here that would be great.

Q. A cyclist undergoes three successive displacements. First is 120m at 40 degrees North East. Second is 82m at 72degrees South East and third is 195m at 35 degrees South West.

As I understand it is done in components. Finding the x component and y component of each displacement and then adding all the x components together. then adding the y components together. then squaring both values, add together and the find the square root. then find the angle.
these are the components I get.

Force x component y component
120m 120cos40 = 91.9 120sin40 = 77.1
82m 82cos72 = 25.3 -82sin73 = -78.4
195m -195sin55 = -159.7 -195cos55 = -111.8

r= -42.5 -113

r= square root of (42.5^2 + 113^2) = 120
angle is tan(-1)(113/42.5) = 69 degrees
so my answer is 120m at 69 degrees.

Thats what I get. The answer in the book is 102.7m at 24.9degrees South East. ??

Any help would be great.
thanks
elani
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