aptitude style physics q's

[sasha]

two scenarios

A plane(A) is flying at a constant 300kmph and is 100km away from a plane(B) flying at 200kmph.
when will A overtake B?

Plane A is travelling at a constant 260kmph and is 800m away from plane B travelling at 300kmph in the opposite direction (they're coming at each other), when will they meet?

i completely forgot basic physics -___- and have an aptitude test coming up with similar type q's. what's the quickest way to solve them (no calc). step-by-step would be greatly appreciated, thanks!

[kamil9876]

So we make an axis where at t=0, A is at x=0 while B is at x=100. Hence for A we can write down his position as:

x=300t

while for B his position is:

x=200t+100

Now we just simply solve these simultaenous equations:

300t=200t+100
100t=100
t=1

So after 1 hour.

Second q uses similair reasoning:

We will set that at t=0 A is at x=0 while B is at x=0.8 (we will work in km since most of the quantities here (the two velocities) is given in km/h but either way is fine as long as you are consistent). So for A we have his position-time relation as:

x=260t

while for B:

x=0.8-300t

again solve the simultaenous equations.