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# Help with M1 Question - Final Part Watch

1. I have done part (a) , (b) and (c). Just need help with (d).

A particle starts at origin, O. It moves with constant velocity ( 2i + 3j ) ms-1 for 2 seconds. It then accelerates with constant acceleration ( i - 3j) ms-2 for 6 seconds, before slowing uniformly to rest in 4 seconds.

a) Find it's displacement during the first stage of the journey.

b) Find its velocity after the second stage of the journey.

c) Find its acceleration during the third stage of the journey.

d) Find its position at the end of the journey.
-----------------

a) r = ut + 0.5at^2

r = 2( 2i + 3j) = 4i + 6j ----------- a = 0.

b) v = u + at

v = ( 2i + 3j ) + 6 ( i - 3j )
= 2i + 3j + 6i - 18j
= ( 8i - 15j ) ms-1

c) u = 8i - 15j v = 0 a = ? t = 4

0 = ( 8i - 15j ) + 4a

a = ( -2i + 3.75 )

2. s=ut+0.5at^2
3. Find the position vector relative to the stage before and then add them up.
4. Thank you for the replies guys, however I am still not getting the answer.

With my working out I am getting (62i - 42j). The answer is (50i + 60j)

I really don't know where I am going wrong.
5. Stage 1:
(4i+6j)

Stage 2:
= (2i+3j) . 6 + (1/2)(i-3j)(36)
= (12i+18j) + (18i-54j)
= (30i-36j)

Stage 3:
= (8i-15j)(4) + (1/2)(-2i + 3.75j)(16)
= (32i-60j) + (-16i + 30j)
= (16i-30j)

(50i - 60j)
6. Thank you so much! I just got it however, I was like, it's -60j and the answer was +60j.

I assume the book is now wrong. Really appreciate your help. Thank you

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Updated: July 6, 2014
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