2. Impulse-Momentum Theorem
The impulse due to all forces acting on an object (the net
force) is equal to the change in momentum of the object:
Fnet t= p
We know the units on both sides of the equation are the same,
but let’s prove the theorem formally:
Fnet t = mat = m ( v/t) = m v = p
3. IMPULSE
Is the product of a force and the time
the force acts on.
Impulse is a way to measure a change
in momentum .
4. A change in
momentum in a
short time
requires a large
force.
A change in
momentum in a
long time
requires a small
force.
5. Force and Momentum Change
To find the impulse, you rearrange the momentum form of the second law.
I =Ft (Ns) p =mv (kg m/s)
I = p
Ft=mv
6. Sample problem:
1. A 50 N is applied to 100kg boulder for
3s. Solve for the impulse.
I =Ft
F= 50 N
T= 3 s
I =
I = 150 Ns
50 N (3s)
7. Sample problem:
2. A 0.10 kg model rocket’s engine is designed to deliver an
impulse of 6Ns. If the rocket engine burn for 0.75s, what is the
average force does the engine produce
F=I/t
I= 6 Ns
T= 0.75s
F=
F= 8 N
6 Ns /(0.75s)
Take note!
I=f t
F=I/t
t
t
8. Sample problem:
3. A bullet traveling at 500 m/s is brought to rest by an
impulse of 50 Ns. What is the mass of the bullet?
I = p
I =m v
m=I/v
I= 50 Ns
v= 500 m/s
m=
m= 0.1 kg
50Ns/(500 m/s)
Take note!
1N= 1 Kg m/s
Kg m s
s
m/s
2
9. Let’s have a practice:
1. A football player kicks a ball with a force of 50N. Find the impulse
on the ball if his foot stays in contact with the football for 0.01s.
I = Ft
F = 50 N
t= 0.01s
I =
I = 0.5 Ns
50N(0.01s)
10. Let’s have a practice:
2. Aunt Mary needs to hang a picture in her bedroom. She uses a
hammer to drive the nail into the wall. Find the force exerted by the
hammer on the nail if the hammer stays in contact with the nail for
0.5s and has an impulse of 25Ns.
F=I/t
I= 25 Ns
t= 0.5s
F =
F = 50N
25Ns/(0.5s)
11. Time for quiz:
1. A hockey player applies an average force of 80N to
a 0.25kg hockey puck for a time of 0.2s. Determine
the impulse experienced by the hockey puck.
2. A 0.5kg baseball experiences a 10N force for the
duration of 0.1s. What is the change in velocity of the
baseball?
3. A space shuttle burns fuel at the rate of 13,000kg in
each second. Find the force exerted by the fuel on the
shuttle if in 2s the shuttle experiences a change in
momentum of 325,000kgm/s.
2. V=FT/M
3. F=P/T
