# Thread: Meeting point between two vehicles

1. ## Meeting point between two vehicles

Driver A starts his car and accelerates with a constant accelerasion of 0.8 m/s^2.
Driver B starts and follows on a motorcycle from the same spot, 6,0 sec later.
Driver B has got a constant acceleration of 1.8 m/s^2. (Neither of them accelerate higher than 80 km/h)

a) How long does it take driver B to catch up with driver A?
b) How long have they driven when they meet?
c) How fast do each driver drive when they meet?

I have tried the four formulas:

v = at+v0

s = 1/2 (v+v0) * t

s = 1/2 a * t^2 + v0 * t

2 * a * s = v^2 - v0^2

With no luck at all. I am confident that some calculations might be wrong.

All help is appreciated, hopefully a quick response.

2. ## Re: Meeting point between two vehicles

Originally Posted by roahau
Driver A starts his car and accelerates with a constant accelerasion of 0.8 m/s^2.
Driver B starts and follows on a motorcycle from the same spot, 6,0 sec later.
Driver B has got a constant acceleration of 1.8 m/s^2. (Neither of them accelerate higher than 80 km/h)

a) How long does it take driver B to catch up with driver A?
b) How long have they driven when they meet?
c) How fast do each driver drive when they meet?
for driver A ...

$v_A = 0.8t$

$s_A = 0.4t^2$

for driver B ...

$v_B = 1.8(t-6)$

$s_B = 0.9(t-6)^2$

for (a) and (b) , set $s_A = s_B$ , solve for t to find the time driver A's run ... don't forget that driver B's run is $(t-6)$. once you get the time, find the value of $s_A$ and $s_B$ (which should be the same, right?)

for (c) , determine the values of $v_A$ and $v_B$ at the time found above.

3. ## Re: Meeting point between two vehicles

Originally Posted by skeeter
for driver A ...

$v_A = 0.8t$

$s_A = 0.4t^2$

for driver B ...

$v_B = 1.8(t-6)$

$s_B = 0.9(t-6)^2$

for (a) and (b) , set $s_A = s_B$ , solve for t to find the time driver A's run ... don't forget that driver B's run is $(t-6)$. once you get the time, find the value of $s_A$ and $s_B$ (which should be the same, right?)

for (c) , determine the values of $v_A$ and $v_B$ at the time found above.
How am I supposed to determine t without the values of vA and vB ? I can't use the first formula without time, and I can't use the time forumula without the final velocity

4. ## Re: Meeting point between two vehicles

Originally Posted by roahau
How am I supposed to determine t without the values of vA and vB ? I can't use the first formula without time, and I can't use the time forumula without the final velocity
when the two vehicles meet, they are at the same position.

$s_A = s_B$

$0.4t^2 = 0.9(t-6)^2$

solve for t , then proceed as I stated in my previous post.