# Homework Help: Impulse, I have found a, b and d

1. Oct 22, 2007

### snipaj9696

The magnitude of the net force exerted in the x direction on a 3.15 kg particle varies in time as shown in the figure below.

There is a graph that is supposed to be here. The y-axis is F(N) and the x-axis is t(s)
It starts from the orgin then goes to point (2,4), then to (3,4), then ends at (0,5). Im sorry if this looks confusing, but it wouldnt let me post the graph.

(a) Find the impulse of the force. The answer to this one is 12.0 N-s

(b) Find the final velocity the particle attains if it is originally at rest.
i m/s

(c) Find its final velocity if its original velocity is -3.4 m/s .
i m/s

(d) Find the average force exerted on the particle for the time interval between 0 and 5.00 s.
N

so far I have done..

for part A I found the answer to be 12 (4+4+4)

for part B I did I=mv which came out to v=3.8m/s

I am stuck on part c. I thought I am supposed to use I=m(vf-vi) but I keep getting a wrong answer.

And for part d I used I=f(tf-ti) and found the answer to be 2.4N

So I need part c!!

2. Oct 22, 2007

### qspeechc

F=ma; a=F/m v(f) = v(i) +at
Do that for each section.