Question

A 3kg object has a 20N force applied to it for 3 seconds.
-How fast is the object traveling at the end of the 3 seconds?
-If it started from rest, how big an impulse did the object experience?

Answer 1

1) 20 m/s

First of all, we can find the acceleration of the object using Newton's second law:

$F=ma$

where

F = 20 N is the force applied

m = 3 kg is the mass of the object

a is the acceleration

Solving for a,

$a=\frac{F}{m}=\frac{20}{3}=6.67 m/s^2$

Now we can find the final velocity of the object using the suvat equation:

$v=u+at$

where

u = 0 is the initial velocity

$a=6.67 m/s^2$ is the acceleration

t = 3 s is the time

Substituting,

$v=0+(6.67)(3)=20 m/s$

2) 60 kg m/s

The impulse exerted on the object is equal to its change in momentum:

$I=\Delta p = m(v-u)$

where

m is the mass

v is the final velocity

u is the initial velocity

For the object in the problem

m = 3 kg

u = 0

v = 20 m/s

Substituting,

$I=(3)(20-0)=60 kg m/s$