# Homework Help: P = F delta T!

1. Jan 12, 2006

### metalmagik

okay Im not sure what the right answer is out of these multiple choices because Im not sure how exactly to use F delta T.

A 4.0-N force acts for 3.0 sec on an object. The force suddenly increases to 15 N and acts for one more second. What impulse was imparted by these forces to the object?

a. 12 Ns
b. 15 Ns
c. 16 Ns
d. 27 Ns

I got like...both A and B as possible answers but im not sure which one is right..I used F delta T to get 12 because I just did 4 x 3. Then I got 15 by doing 15 x 1. Im not sure how to use the change in time... when i played around with it i was getting numbers that were not any of the choices. Any help is much appreciated.

2. Jan 12, 2006

### StatusX

Impulse is additive. That is, if you have an impulse of A over one period of time, and an impulse of B over another period, then the total impulse over both periods is A+B. (taking into account the direction each time)

3. Jan 12, 2006

### metalmagik

Thanks! Let's hope I do good on this re-test after I bombed the first momentum test. haha