# Final velocity, three forces, time, mass and velocity given

## Homework Statement

A small robotic spacecraft (m= 145kg) is initially moving in the +x-direction at .150 m/s. Then, its x-axis thruster exerts the following force on the spacecraft:
Fx(t) = -5.00 N during 0s<t<1.5s
-9.00 N during 1.5s< t< 3.25s
-6.00 N during 3.25s <t< 4.00s
When the thruster stops firing at t=4.00s, what is the spacecraft's final velocity?

v= mt2

## The Attempt at a Solution

well...don't you have to find the displacement/"?

Well, you can find the deceleration of eachtime interval with Newton's second law, then go from there.

HallsofIvy
Homework Helper

## Homework Statement

A small robotic spacecraft (m= 145kg) is initially moving in the +x-direction at .150 m/s. Then, its x-axis thruster exerts the following force on the spacecraft:
Fx(t) = -5.00 N during 0s<t<1.5s
-9.00 N during 1.5s< t< 3.25s
-6.00 N during 3.25s <t< 4.00s
When the thruster stops firing at t=4.00s, what is the spacecraft's final velocity?

## Homework Equations

v= mt2
What??? where did you get this? It doesn't even have the right units: v is m/sec and mt^2 (which I guess you mean) is in kg sec^2. I think you meant F= ma. And then v= v0+ at.

## The Attempt at a Solution

well...don't you have to find the displacement/"?
No, you don't. It is not asked for and you don't need it to find the velocity, Use F= ma to find a and then use v= v0+ at to find t at the end of each time interval. v0 is the speed at the beginning of each time interval.