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Mechanics 1b Quesiton watch

1. A jet ski is at the orgini and is travelling due north at 5ms-1 when it begins to accelerate uniformly. After accelerating for 40secs, it is travelling due east at 4ms-1

The jet ski is travelling south easy t seconds after it leaves the orgini.
a) find t

so i wrote down an expression for V,

v=5j + (0.1i-0125j)t
= 0.1ti + (5-0125t)j

then i made them both equal, 5-0.125t = 0.1t (but however the mark scheme says its 5-0.125t = -0.1t)

2. (Original post by Gary)
A jet ski is at the orgini and is travelling due north at 5ms-1 when it begins to accelerate uniformly. After accelerating for 40secs, it is travelling due east at 4ms-1

The jet ski is travelling south easy t seconds after it leaves the orgini.
a) find t

so i wrote down an expression for V,

v=5j + (0.1i-0125j)t
= 0.1ti + (5-0125t)j

then i made them both equal, 5-0.125t = 0.1t (but however the mark scheme says its 5-0.125t = -0.1t)

because it is SOUTH east, not NORTH east
3. (Original post by TenOfThem)
because it is SOUTH east, not NORTH east
Ohh right... what would happened if its like south west?
4. (Original post by Gary)
Ohh right... what would happened if its like south west?
then both i and j would be negative
5. (Original post by TenOfThem)
then both i and j would be negative
Ah ok, get it now, thanks

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Updated: January 5, 2013
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