- #1

savva

- 39

- 0

## Homework Statement

Starting from rest, a subway train first accelerates to 25m/s and then begins to brake. Forty-eight seconds after starting, it is moving at 17 m/s. What is its average acceleration in this 48-s interval?

## Homework Equations

1. v=v0+at

2. x=x0+(1/2)(v0+v)t

3. x=x0+v0t+(1/2)at^2

4. v^2=v0^2+2a(x-x0)

## The Attempt at a Solution

I am unsure of this question here - I tried drawing the situation in a velocity vs time graph with velocity increasing from rest to 25ms^-1 and then decreasing to 17ms^-1 over 48s. However the question didn't specify the time at which it reached 25ms^-1, I attempted the question without this information but couldn't solve this question. How do you know at what point in this 48s it reaches 25ms^-1 and subsequently it's displacement?

I tried using the equation of motion for constant acceleration but could not find a suitable one.

Thus tried using the average acceleration=[itex]\Delta[/itex]X/[itex]\Delta[/itex]t in hope but I was unsuccessful there.

The answer is 0.354m/s^2