A 1kg body is subjected to a single force F=-6 ·i +8·j N for 5s. If we know that its initial velocity is vo=15 ·i -10·j N. Calculate:


b)Linear momentum before and after the force is exerted.



F=-6 ·i +8·j N
vo=15 ·i -10·j N
Δt = 5 s
m = 1 kg
Linear momentum before applying the force p0 = ?
Linear momentum after applying the force p = ?


Question a)

We know impulse of a force is calculated by multiplying that force by the time  applied, so:

J=F·t J=-6 ·i +8·j N · 5 s J=-30 · i+40 · j N·s

Question b)

By using the linear momentum definition we can calculate the moment before applying the force:

Since the impulse is equal to the growth of the linear momentum when applying the force, and the growth is the substraction of momentum the body has before and after applying the force:

J=p = p-p0p=J+p0 p=-30·i+40·j N·s +15·i-10·jN·sp=-15·i + 30 ·j N·s

Formulas worksheet

These are the main formulas that you must know to solve this exercise. If you are not clear about their meaning, we recommend you to check the theory in the corresponding sections. Furthermore, you will find in them, under the Formulas tab, the codes that will allow you to integrate these equations in external programs like Word or Mathematica.

Related sections
J=F·t =p