# Physics help EMERGENCY!

• Sep 9th 2008, 05:52 PM
bandnerd1892
Physics help EMERGENCY!
I need help with a couple of problems. I really need this soon so any help will really be of service.

Two particles are at the same point at the same time, moving in the same direction. Particle A has an initial velocity of 8.6 m/s and an acceleration of 3 m/s^2. Particle B has an initial velocity of 2.5 m/s and an acceleration of 5.8 m/s^2.
At what time will B pass A?

And:

A subway train starting from rest leaves a station with a constant acceleration. At the end of 6.58 s, it is moving at 16.45 m/s.
What is the train's displacement in the first 4.42834 s of motion?

Thank you sooooooo much!
• Sep 9th 2008, 06:46 PM
skeeter
Quote:

Two particles are at the same point at the same time, moving in the same direction. Particle A has an initial velocity of 8.6 m/s and an acceleration of 3 m/s^2. Particle B has an initial velocity of 2.5 m/s and an acceleration of 5.8 m/s^2.
At what time will B pass A?
both particles will have the same displacement when B passes A.

here is the displacement equation ...

$\displaystyle \Delta x = v_0 t + \frac{1}{2}at^2$

Quote:

A subway train starting from rest leaves a station with a constant acceleration. At the end of 6.58 s, it is moving at 16.45 m/s.
What is the train's displacement in the first 4.42834 s of motion?
$\displaystyle a = \frac{\Delta v}{\Delta t}$

once you calculate acceleration, then you can use

$\displaystyle \Delta x = v_0 t + \frac{1}{2}at^2$

to calculate the displacement.
• Sep 10th 2008, 11:01 AM
CaptainBlack
Quote:

Originally Posted by bandnerd1892

Two particles are at the same point at the same time, moving in the same direction. Particle A has an initial velocity of 8.6 m/s and an acceleration of 3 m/s^2. Particle B has an initial velocity of 2.5 m/s and an acceleration of 5.8 m/s^2.
At what time will B pass A?

We need to know their initial seperation. Then it is a relative velocity problem. The initial relative velocity is 8.6-2.5 m/s and the relative acceleration is 3.0-5.8 m/s^2

RonL