# Homework Help: Vector Dynamics

1. Oct 7, 2011

### yardy_genius

1. The problem statement, all variables and given/known data

An air craft has an initial velocity of 90(i+ j)ms-1and a final velocity of 10(10i + 10j +3k) ms-1. The time taken for this change to occur is 100 s. Determine the:
a)average velocity for the 100 s period.
b)average speed for the period.
c)constant acceleration of the airplane in unit vector notation.
d)magnitude of the acceleration.
e)vertical height the plane has risen.
f)distance plane travelled for the 100 s period

2. Relevant equations

3. The attempt at a solution

I have calculated all the above but i am confused as to which one of the vectors to state as the variable.

using the formula S= ut + 0.5at^2

i got the unit vector form (9500i + 9500j+ 1500k) this is correct.

now the solution says the vertical height is 1500k, but i thought 9500j was the vertical component. can some please explain this to me.

my answer
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 7, 2011

### Staff: Mentor

I think you must be picturing the x-y-z axes as representing, let's say, x for eastward, y for up (as in altitude), and z for northward? That could feasibly be true, but for the velocity here rising to 100i + 100j + 30k it would be more like a ride on fighter plane, gaining 100m in altitude for every 104m you travel over terrain. If you instead interpret z as representing altitude, then plane passengers will be less terrified.

I'm not saying I'm correct, but it seems the question does leave this up to you to decide. Which means there is room for ambiguity.

Last edited: Oct 7, 2011
3. Oct 7, 2011

### yardy_genius

thanks, i was kinda thinking along those lines too...

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