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(Edexcel) M1 Vectors question

1. At 2pm the coastguard spots a rowing dinghy 500m due south of his observation point. The dinghy has constant velocity (2i + 3j)ms^-1.

a) Find in terms of t, the position vector of the dinghy t seconds after 2pm. Answer is 2ti + j(3t-500)
b) Find the distance of the dinghy from the observation point at 2:05pm.
s = vt
s = s
v = sqrt(13) -- calculated from sqrt(2^2 + 3^2)
t = 5 x 60 = 300 -- since we want time in seconds.
therefore s = sqrt(13) x 300 = 1081.7m

however, according to the answer page, the distance is actually 721m. any ideas where i went wrong? thanks
yo nigs..
dumb maths student
1. At 2pm the coastguard spots a rowing dinghy 500m due south of his observation point. The dinghy has constant velocity (2i + 3j)ms^-1.

a) Find in terms of t, the position vector of the dinghy t seconds after 2pm. Answer is 2ti + j(500+3t)
b) Find the distance of the dinghy from the observation point at 2:05pm.
s = vt
s = s
v = sqrt(13) -- calculated from sqrt(2^2 + 3^2)
t = 5 x 60 = 300 -- since we want time in seconds.
therefore s = sqrt(13) x 300 = 1081.7m

however, according to the answer page, the distance is actually 721m. any ideas where i went wrong? thanks


I think the mistake is simply that the answer to a) should be

x(t) = 2ti + j(3t - 500)

because the boat is 500m due south, i.e. in the negative y direction.

To confirm this, check what position x(0) gives...

Also not quite sure of your method for part 2; all you need to do is find |x(t=300)|
spread_logic_not_hate
I think the mistake is simply that the answer to a) should be

x(t) = 2ti + j(3t - 500)

because the boat is 500m due south, i.e. in the negative y direction.
are you retarded?

j(3t - 500) = 3tj - 500j (i.e. 500m in the negative y direction).

i have my answer anyways. go revise, i think u need it
dumb maths student
are you retarded?

j(3t - 500) = 3tj - 500j (i.e. 500m in the negative y direction).

i have my answer anyways. go revise, i think u need it


You've posted

Answer is 2ti + j(500+3t)


Sorry for trying to help there...

Also thanks but i've passed my exams already :smile:
spread_logic_not_hate
You've posted



Sorry for trying to help there...

Also thanks but i've passed my exams already :smile:
so why are you crying? i detect failure.
this kid is funny.. editing a quote from my post to make it look as if he isn't retarded

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