Today, I discussed the Conservation of Momentum.
According to the Conservation of Momentum, the momentum initially is equal to the momentum
finally.
pi = pf
From Chemistry, you might remember the Conservation of Matter and Energy which states that
matter and energy cannot be created or destroyed. What you start with is what you end with.
The same thing holds true for momentum.
We will be using the two following equations:
m1 v1i + m2 v2i = ( m1 + m2 ) vf
m1 v1i + m2 v2i = m1 v1f + m2 v2f
Do not let the equations stress you out. Look at them carefully.
1st - m v is momentum
2nd – i refers to initial and f refers to final
3rd – the 1 and the 2 refers to the objects in question
Let’s see how this works in a problem.
#1: A 25 kg boy moving with an initial speed of 3.5 m/s jumps onto a 3.2 kg skateboard
at rest. What is the speed of both the boy and skateboard when they move off together?
Two objects: 1 is the boy and 2 is the skateboard
We use the first equation because they are together with one final speed at the end.
m1 v1i + m2 v2i = ( m1 + m2 ) vf
*both have the same speed because
they move off together
So, solve for the final velocity of the boy and the skateboard.
Show Work Here: m1 v1i + m2 v2i = ( m1 + m2 ) vf
#2: Solve for the final speed of the boy if he slips off the skateboard instead off being on the
skateboard. You need to know that the final speed of the skateboard is 2.1 m/s. Use the above
initial information about the boy and the skateboard. However, now, the boy has a separate final
speed and the skateboard has a separate final speed.
Equation to be used: m1 v1i + m2 v2i = m1 v1f + m2 v2f
* *
Two separate final speeds
Show Work Here: m1 v1i + m2 v2i = m1 v1f + m2 v2f