# Homework Help: Force given by a vector

1. Oct 14, 2008

### kennien

The force acting on a object ( 10 kg ) as function of time is given by :

F (t) = [ (-20t + 90)i - 60j + ( 10t + 40)k ] Newton

At time t=0 seconds , the speed of the object is given by :

V = [-14i + 26j + 32k ] m/s

question a )

use the impulse-momentum theorem for deciding the objects speed at t=4 ?

question B )

What is the average force acting on the object in the time interval t=0 -> t=4 ?

I can probably solve this task , but when I must use the theorem , I kind of get stuck

No examples of the use of this have I found online , not in textbook either

2. Oct 14, 2008

### tiny-tim

Welcome to PF!

Hi kennien! Welcome to PF!

The impulse-momentum theorem is the impulse version of Newton's second law, F = d(mv)/dt.

Instead of force = rate of change of momentum (the ordinary version), the impulse version is impulse = total change of momentum (I = m∆v).